why is my startup disk full when I do not have stuff on it

I have gone through my Mac Pro and I cannot understand why my startup disk us full. I emptied trash and practically saved all my files on memory sticks.

In the Mac information it says that 'other' is using up 200GB. I don't know where to search for 'other'.

Also everytime I try to delete files, 'other' gets fuller. It went from 170 to 200 and all I was doing was deleting. Is there another trash can somewhere?

Please help