How do I use my registry cleaner the right way?

I don't want to accidentally delete something I need, like a document in microsoft word that I want to keep for example. I downloaded the free CCleaner because my computer has been running slowly and I found out about registry cleaners, I've never used one before. After I analyzed my computer with ccleaner it lists a bunch of stuff. In recent documents section, it lists names of my documents, some of which I want to keep, but the size is only 1 kb and when I go to the actual document in MW that size is like 500 kb. When I click on the 'file' from ccleaner it says it's just a shortcut. So am I safe with just going ahead and letting it clean up? Does it delete anything important or does it just get rid of the unecessary stuff automatically? I hope I explained this well enough to be understood. I just don't want to mess up my computer!