I thought they were automatic ie not generated by your previous searches but by google itself...I always get a huge list of stuff that i've never looked for and no one else uses my pc eg if I put in "un" I get things like underfloor heating and underactive thyroid, neither of which I've ever searched for!!
You can highlight the words and then delete them with the delete key. There is probably another way to find out where you have been but I don't know. I struggle with surprises for my DH when I do things on-line as he's an IT manager and always looks to see where I have been