my ssd is full of invisible files

I installed Sierra (macOS10.12) on a 2012 MacPro computer.

I added a Crucial 1TB solid state hard drive as my start up drive.

I have about 20 GB of files on the SSD --- but I and getting warnings that my SSD drive is full

If I open the drive I can see my folders --- Sierra stuff, Photoshop and mail. About 20GB of applications and data.

If I choose the SSD under "get info" it says that I have 1.05 TB but I am using 1.01TB .....

I used a program to examine the SSD and it shows that I have a small part of the drive used for applications - there is no music or photos. BUT - it shows that there is a 1TB section it callls "other."

My user folder shows as being 1TB - - but i can't find any folder in it that is 1TB ....

What is filling up my SSD and how do I make it go away ???

Richard