Hi Suzanne,
Thank you for the screenshot, everything on your drive is nominal size, with the exception of the Users folder, that is taking up 3/4 of your drive space.
So, you need to dig down into that folder with TreeSize to find where that space is being used, I cannot see the bottom of the TreeSize window, but I assume you have a 120GB SSD (118GB Writable space) and you need to clear at least 20GB of space from that drive.
SSD drives need to be minimum 1/5 free space ot be efficient and to prolong the lifespan of the drive.
Please dig down into that user folder in TreeSize. and let me know what you find.