how do I delete stuff on my disk

Delete user data only ... that which you create or downloaded. You can also uninstall 3rd party apps but they usually don't take up much space.

The usual solution is to move user data to an external drive, verify the data then delete it on the main drive. Audio-visual files are the biggest file you have most likely

However, be aware of purgeable. If you delete a large chunk of data your Mac will likely sequester that data in Purgeable space and open space does not appear to grow larger. Apple says the space will be available when needed.

https://www.macobserver.com/tips/how-to/macos-purgeable-storage-hard-drive/

I use paid Daisy Disk to reduce purgeable when needed.