Quick down and dirty guide to "armors" of SRO.
There are 3 "armor types" in the game. Armor is the name of the heaviest type. It offers the most physical defense and the least magical defense.
Protector, also known as leather, offers less protection then Armor in terms of physical defense but more magical defense. It is also lighter armor so can gain a light bonus if you wear all Protector pieces. You can mix and match Protector pieces with Armor pieces but I wouldn't recommend it. Go with one or the other. The bonus you get from wearing all protector is a 10% run speed increase and a reduction of 10% of the mana cost of all your skills and spells. So if a skill would normally take 20 mana points to use it instead takes 18 mana points. Remember ALL pieces must be Protector to make use of this bonus and you must have all slots that are available to wear "armor" filled. If you are missing your helmet piece then you do not get the bonus even if you have Protector on every other spot.
Garments can not be worn with any other piece of armor. It can not be mixed and matched with the other "armor types." It offers the least physical resistance and the most magical resistance. It is also much lighter and thus gives a bigger bonus when all "armor slots" on your character are filled with Garments. The bonus is a 20% run speed increase and a 20% mana reduction when using skills so a skill that takes 20 mana points will instead take 16.
Personally, I recommend every one start off with Garments until level 20. The difference you see in the physical resistance between the different "armor types" is negligible. The difference you see in the mana potions or downtime you have is immense, especially when you are low level and strapped for cash. That 20% mana reduction bonus from Garments will make a bigger difference in your leveling speed from lack of downtime and cut down on your mana potions that you'll need to use.
Now the armor sets come in 3 tiers just like weapons. I'll explain using weapons because it's easier to see since you only have one weapon slot but 6 armor slots. Take a Bronz Bow for example. This is a level 8 bow as sold by the blacksmith in Jangan. The next level bow sold by the blacksmith is an Iron Bow for use by level 16. Does this mean you are stuck using a Bronz Bow from level 8 through 15? No. There are multiple tiers to the Bronz Bow but the other two tiers are dropped by monsters and not sold in shops. The other two tiers of a Bronz Bow are Hunter Bronz Bow which is level 10 and Archer Bronz Bow which is level 13. This gives players 2 stepping stones on the way to 16. Iron Bow has the same steps. Level 16 is sold by the shops, but level 18 and 21 is dropped.
Armor sets follow the same pattern as weapons in that they have tiers but since there is 6 armor slots: chest, legs, head, hands, shoulder, and feet; each slot is not the same level. Let us take Small Linen Garments for example. This is roughly the level 8 armor sold by the NPC shop vendor. However, not all slots are level 8. They are in the following increments: Small Linen Gloves are level 8, Small Linen Shoulders are level 9, Small Linen Feet are level 10, Small Linen hats or crowns (depending on if you want to see your head or not because you get a choice of which style headwear to use) is level 11, Small Linen Legs are 12, and Small Linen Chestpieces are 13.
Just like weapons there are also difference tiers of armor sets. For Linen for example it starts with Small Linen as sold by shops. The next tier is Half Linen, and the last tier is Complete Linen. Usually by the time you are wearing the Small Linen Chest piece you are wearing a few pieces of Half Linen on the lower level armor slots like the hands and shoulders. By the time you are wearing a Complete Linen Chest piece you can equip the starting tier of the next higher armor set which is Sungyon Silk for the hands, shoulders, and feet.
That's the basics of armor for SRO in a nut shell. The more complex task is looking at the stats of each armor item you want to wear and deteremining whether you are putting on something exceptional or something rather ordinary. There are many things to look at. The biggest in my opinion and the least though of stat is the Parry rate. Each piece of armor in SRO has a parry rate listed on it. The higher armor sets have higher rates. What parry does in SRO is not like the parry rates of other games. It does not stop incoming attacks. Instead, it deflects the damage range of an incoming attack.
At this point if you read the above sentance you might be wondering what the hell I'm talking about. Well lets have an example.... In this example we'll use two opponents, an Attacker and a Defender.
An Attacker is using a weapon with a physical damage range of 100-150. If the defender was wearing no armor at all and this was a rather static environment, the damage dealt would fall somewhere inbetween 100 and 150 for each attack made. The average damage would be 125 in a perfect world. If the defender is wearing armor that gives a physical resistance of say 50, then the damage recieved would be reduced by 50 points. This makes the damage range of the attacker now 50 to 100 with an average hit of 75. Still so far, this is pretty basic.
Now SRO throws us a curve ball by implementing is own special brand of Attacking Rating and Parry Ratio. These two numbers are compared for each attack made by the attacker and the defender. Based upon the comparison the average damage is "shifted" in one direction or another. Still using the above example, we'll add Attack Rating and Parry Ratio into the mix. If the Attacker has a rating of 100 and the defender has a parry of 100 then the average damage would remain 75. Now, if the defender had aparry skill of 150 compared to an attack rating of 100 then the average damage would slide down to 50 damage. This isn't getting rid of the damage range of the attacker. It is still 100 to 150 minus 50 armor so 50 to 100. Hits for 100 are still possible. However, when a hit is made, a random roll occurs. The roll is the "weight" of the difference between attack rating and parry ratio. If the roll is in favor of the defender, the damage that would normally occur is instead reduced but never exceeds the minimum. If the roll is in favor of the attacker the damage is increased but does not exceed the max damage. If the Parry Ratio is higher then that random roll is going to occur more often favorably for the defender. If the attack rating is higher, then it is going to occur more favorably for the attacker. Just think of a shifted bell curve from statistics.
The effect of having a higher parry ratio is rather astounding in the low levels when the physical resistance between Garments and Armor sets are very minimal. A full set of Small Linen Garments will have a physical resistance of around 24.7 if bought directly from the store. A full set of Infantry Bronz Armor of the same level will have a resistance of 30.1ish. That 5.4 points of damage reduction is not that much of a difference to out weigh the benefits of Garment armor at lower levels. At higher levels, the difference becomes great enough that for melee users, going with protector or armor will severly cut down on the damage recieved by physical sources.
All stats on items have a variance to them when you find one off a monster. So while the basic Small Linen Gloves that are level 8 as sold by the shop might have a physical resistance of 2.5 and a parry ratio of 5; those same gloves as dropped by a monster could have more or the same for either stat on that armor piece. More parry is a good thing
Now there are also other factors involved in the damage done during an attack. Stuff like physical balance versus magical balance based on the stats you chose will determine your weakness to either magical or physical damage. The physical reinforcement and magical reinforcement numbers on armor pieces I still have zero clue about. They don't seem to do anything so I've been largely ignoring those numbers up to now. You can test and see the effect of the other numbers very readily. I'm sure those numbers do something, and the higher the number the better I suppose but I can't tell you for sure what those percentages listed there mean.