Currency in world of tanks comes in two forms, Gold and Experience points.
Gold is a premium kind of currency in World of Tanks. They can be traded for credits, used to turn elited exp into free exp. These kinds of currency are usually earned by purchasing them in the WoT store, Clan War territories and fun Contests.
Credits(or Silver) are the most basic form of currency in World of Tanks. They are earned via battling in battles. Can be received from gold exchanges and are essential to play. They allow you to purchase new tanks, modules ammo, camo, emblems, and repair tanks.
Experience Points are used for researching new tanks and modules. They come in two kinds, free and tank. Free Points can be used on anything that you can research. Tank Points can only research things that are in that tank's research tree.