Each nation has its own particular take on currency, but there are similarities they all share. Primarily, each has three types of coin made from gold, silver, and copper. Currency is generally accepted in any nation, though it may raise an eyebrow or two depending on the cultural and political climate of your campaign.
A gold coin is worth 10 silver coins.
A silver coin is worth 10 copper bits.
When a player begins the game, they would usually receive a sum of money to purchase an initial set of equipment for adventuring. The formula for starting currency is:
4d6 x 10 gp
Each player would roll the above formula and use the resulting money to purchase starting equipment. Alternatively, the GM may decide to simply hand out the average, 140 gp to each player equally.