They are a type of currency for the seasonal classes such as the wild card, the expert coder, and developer
all of these classes you choose to earn your coins will come at a cost of playtime.
they have once planned a shop where you can spend code streaks or skins this is not in the main game though, so you'll see once version 0.5 comes out.
(this page was changed because the developer changed the schedule of the shop because it's working but in stages.)