The various grades also offer armor sets, which you can see here:
http://lineage2.stratics.com/content/library/sets/
See people almost never look through the library on the official forums, tut tut...
You can see all the special armor sets right here (
http://www.lineage2.com/Knowledge/item_sets.html) on the official site, including the option to view it on a charcter of your race and sex.
All pieces of armor (both sets with and without bonus) can be seen here (
http://www.lineage2.com/Knowledge/item.html?category=armor) again on the official site and with screenshots.
Or you can just go "The Library -> Items & Equipment -> Armor"
About your armor, since your lvl 13 you can only wear robes or light armor (if you want to wear light armor efficiently you should buy at least the first light armor mastery from your skill trainer).
However untill Piece bone Breastplate and Gaiters and Bronze armor (which you shouldn't be able to afford just yet) the No Grade armor with the most P.def is Light armor, so just wear that. When you reach lvl 14 you can buy Heavy Armor mastery from your skill trainer, so if you can afford Piece Bone or Bronze armor after lvl 14, get at least the first Heavy armor mastery and you'll be able to wear it efficiently.
20-40 You can wear robes if you can get groups regularly and you really need the + mana but the best thing is to stick with D grade heavy armor and maybe if you can afford it have a backup devotion set (+15% cast speed) for when you buff.
40+ It really depends on which class you choose and which playstyle fits with that. Once you get there you can ask the specialists themselves(Warcriers and overlords) which weapon + armor they think is best.
One last thing. When some time after lvl 20 you get to the top No Grade armor and weapon and you see you can start to afford D Grade be aware that you can't upgrade your weapon or armor through the store NPC like No Grade. Although the No Grade population is kinda low you still have a chance to sell your top No grade items to people who reroll, though it might take a few days. But perhaps you want to keep your top No grade for another character in the future.
However you should always be able to sell your D grade armor and weapons for a fair price since dwarfs can make crystals out of them. Additionally you can upgrade your weapons through the merchant of mammon with Ancient Adena, however that's a whole other story together with the seven signs competition and you shouldn't have to do that in the begginning since it's quite expensive.
Also when you buy higher D grade armor or weapons from other people always make sure you either check the price in the shop in dion or if it's higher in Giran or Heine which have the highest store bought weapons and armor.
If you can't find it in Giran or Heine NPC shops it's not buyable from shops and you should ask friends or here on the boards if it's a fair price. For example special pieces for the Highest D grade sets, like a Brigadine Helmet are severely overpriced and just not worth it. So are the Highest D grade weapons, the prices are just way out of proportion, except the dual swords, which you should always make yourself unless you see them for 2.1 mill or under.
I hope with this I have also awnsered some of your fututre questions.
Also look at "The Library -> Races, Classes & Skills -> Orc"
and then click on the skills tab followed by the " Orc Mystic (
http://www.lineage2.com/Knowledge/race_orc_skill.html?my_class=orc_orc_mage) " tab and after lvl 20 the " Orc Shaman (
http://www.lineage2.com/Knowledge/race_orc_skill.html?my_class=orc_orc_shaman) " tab to see what skills you can get in the future.