You don't "close" tools, you simply switch to another tool. You might want to read the online help on such basics. If for some reason tools "get stuck", which has been known to happen, then you have to provide technical info about your system, your version of PS, your input devices and so on so people can help you figure out what the issue may be.
Just expanding on what @Mylenium has already stated.
The "default" tool in Photoshop is the Move Tool. It sits at the top of the Tools panel and has the keyboard shortcut of "v". When you are finished using different tools you could get into the habit of tapping the "v" key.