free space on macbookair

How to free up storage space on your Mac - Apple Support

https://support.apple.com/en-us/HT206996

See used and available storage space on your Mac

https://support.apple.com/guide/system-information/see-available-storage-space-syspf9b375b9/10.14/mac/10.15

Empty your Trash — Delete files and folders on Mac - Apple Support

https://support.apple.com/guide/mac-help/delete-files-and-folders-on-mac-mchlp1093/mac

User tip: "Other and What Can I Do About It ?"

https://discussions.apple.com/docs/DOC-5142

Try something like OmniDiskSweeper for a GUI to get a good look at itemized file size and location:

OmniDiskSweeper http://www.omnigroup.com/more

The files that you have control over are located in the Documents, Downloads, Pictures, Music and Movies folders.  You can use either of these two free apps, GrandPerspective  or OmniDiscSweeper, to find the largest files on your drive so you can determine if they can be deleted or moved to an external HD for storage.  

Note: you can empty the Downloads folder after the apps and/or updates that were downloaded have been installed or applied.  Many users have found a couple of Gigabytes of files in their Downloads folder which are no longer needed.