Currency is an "item" gained from doing quests or killing monsters, although it could be gained from killing other players in RvR. Currency can be traded for useful items; like armour, health recovering items, and weapons.
The currency used will be common to all factions, and will be divided into gold, silver, and brass coins. When you have 100 brass coins equals 1 silver coin, and 100 silver = 1 gold. Money always "shifts" between brass-silver-gold automatically, so you won't ever see more than 99 brass or 99 silver.
Commonly, you will have accumulated your first silver coin by 2nd or 3rd level, and your first gold coin by level 7 or 8.
You can use the in-game mail system to send or receive money between characters.
Note: Mythic actively bans the accounts of gold sellers, and will suspend or ban the accounts of gold buyers if it is brought to their attention (and they confirm it).