Credits are Trove's premium currency. Like Cubits, Credits are account bound and are unable to be traded. However Credit Pouches may be purchased for real life money and traded to other players via the Player Marketplace. These pouches then may be used to earn credits (250 per pouch).
The easiest way to get them is to buy them for real money in the Store, which supports the developers of the game. Small amounts of Credits can also be obtained at certain Mastery rank achievements. Beginning at Mastery rank 31 and each 5 ranks after that until mastery 100 will give 100 Credits.
The final way to get Credits is to create content for the game; submissions for weapons, hair, decorations, faces, & hats are always open. Submitting creations to the Trove Item Submission Subreddit and being approved will grant users 500 Credits.