Storage NPC's allow you to access a warehouse, where you can store and organize items you don't want in your inventory. Additionally, there is a small amount of account storage, which all of your characters, on the same server, can access.
The Weapon Merchant will allow you to purchase low grade weapons.
The Armor Merchant will allow you to purchase low grade armor.
The Accessory Merchant will allow you to purchase low grade accessories.
A Misc. Merchant sells HP, MP, and Astel HP potions, as well as Resurrection Scrolls, and Return Scrolls for specific locations.
Material Merchants sell components necessary for crafting. If you can't find the right material from a Material Merchant, such as cooking components, check the town to see if there is another nearby.
The Special Merchant is an Ancient Fragment Merchant, who will sell you select pieces of gear for the ancient fragments you get via questing.
The General Merchant will allow you to purchase HP, MP, and Astel HP potions, as well as Regen Food.
You can use the Teleport Manager to easily travel long distances between towns. At a main city, you can teleport to main cities in other regions.
When you die, you gain resurrection sickness. If you visit a Healer, they can remove the Resurrection Sickness for a small fee.
Visiting an Auctioneer will allow you to access the Auction House, where you can buy and sell items to other players.
If you want to create or disband a guild, go visit a Guild Manager.