It's a site that hosts webcomics. The coins allow you to read ahead of release schedule and into the buffer episodes for currently ongoing series, or in the case of finished comics it's usually one episode per day unless you pay coins to unlock the rest right away. Since the site and app is free to use the coins system is what finances the whole thing, outside of ads that is.
But I think we're now also allowed to straight up pay coins as a direct donation if you like an author, even if they don't do the paywall thing, kinda like a forceful gift XD