Can't move my f2 pawn?

Hello! I'm new to chess and just trying to learn the rules, this is a game I played with a computer.

Is there any reason as to why I can't move the pawn in the space f2? I wanted to move it up so I could go further with my knight. I tried to search it up and it said something about "pinning" but I've got no idea what that means!!

If anyone could explain it would be very helpful

Was there a black bishop on c5, and were you castled? If so, you couldn't move the pawn because that exposed your king to check. So the pawn is "pinned" until one of those pieces moves away. As long as that's not happening and there's room in front of that pawn, you can definitely move it whenever you want.