Is powerpoint in windows free?

Because somehow some classmates asked if it cost money and they said (no) but I think they all have laptops and I try it on the iPad…

No.

Unfortunately, PowerPoint is not free

So you can download the app, but then you only have limited access to the functions and the whole thing doesn't work so well. There's a Microsoft annual package that costs 69 euro. This is the best version that you can work with most productively. Our school provides us with this free of charge. Maybe you don't have to ask your teachers about that…