ELI5 I don’t understand how credit cards work

Please explain this to me in a simple way, because I already searched for some info and still was confused.

I got a credit card a while ago, which I paid in full but then started to use again. I did some shopping of items online which I got returned, and the refund went back to the card. The refunds should bring down the money I owe by a lot, meaning it would have again been paid. However, two monthly statements later, the amount show that I owe is still the same as when I start spending. I can’t wrap my head around this. The balance on the last statement remains the same, which is quite high… when the refunds I got should have brought it down. Now I still ow the same.

How does this work? And yes, please explain me like I’m fine please because I wanna pay this card in full

Thank you