traces > visited webpages, cookies etc
auto complete form > have you ever used google many times or similiar? when you type into that same box a list of your recent typed items appear, they will be removed
> registry finds obsolete keys and invalid references, its normally ok to delete these as long as you have backed up your registry
> self explanatory i guess
> recycle bin, any context menu is the menu you get when you right click the icon
Does this help?