How to clear hard drive space on macbook air when storage is full?

I've been using my MacBook Air for a couple of years now and lately I get constant warnings that my storage is almost full. It's gotten to the point where my Mac is running noticeably slower, apps are freezing, and I can barely download or save anything new. I know I need to free up some space but I'm not sure where to start.

Already had a look through my files but I can't figure out what's taking up so much space. The problem is that I don't fully understand what it contains or whether it's safe to delete. I'm also not sure if there are any built-in macOS tools that can help me identify and clean up the biggest culprits.

Could anyone guide me through the safest and most effective ways to clear hard drive space on mac? I'd love to know which files or folders are safe to delete, whether I should move things to an external drive or iCloud, and if there are any trusted free apps that can help.

Beginner-friendly advice would be greatly appreciated. Thank you!