How does the coins system work?

I was reading a BL but the last chapter says it needs 100 coins. Is it required to purchase coins or is there another way of getting coins like for example, levels, XP, or whatever, Cuz I DO NOT HAVE THE FUNDS 😖. Also, if not, do the chapters open up on their own after a certain amount of time like on WEBTOON (on WEBTOON, you wait for a certain amount of days) and other platforms or does it work differently? Cuz I can totally wait!! (I think? )