Currencies

Credits:

The main currency in warframe is credits. Its earned by doing almost anything in the game, killing or completed missions are the most useful ways.

It is used to:

Craft or build items in the foundry

Upgrade mods

Purchase blueprints or items from the Warframe Market.

Platinum:

Platinum is Warframes Paid currency. The main way you obtain it is with real money. However you can also trade parts or mods to players in exchange for their platinum. It is possible to obtain every item in the game without spending money.

It is also used in the warframe market to straight up buy warframes or weapons so you don’t need to craft them or wait for them to build.

You can also trade with other players, you can use platinum to trade for rare items from other players.

Endo:

Endo is used exclusively to upgrade mods. It is earned from killing certain enemies or from mission rewards.

Ducats:

Ducats are only given to you for recycling old prime parts at a ducat kiosk. They are used for purchasing items from baro kiteer who only shows up every 2 weeks.