Hitman Sniper has 2 in-game currencies, Blood Money and Tokens.
Blood Money can be earned by playing missions in Montenegro. Tokens can be earned by playing sessions of Death Valley (Weapons with the Deadly Reward perk will earn Tokens during missions in Montenegro as well)
Both currencies can also be purchased using hard currency. Simply tap the red "+" button next to the currencies at the top right corner of the screen when in the menus. The store will open displaying the offers for the various currency packs available. Some of each currency is also included in the Starter Pack.