Edit: As pointed out in the comments, this doesn't work anymore.
File -> Import Module...
Select directory where you downloaded Volley and follow all of the directions (you probably won't have to change anything, just click "Next" a bunch.)
Then, start typing your volley stuff:
private static RequestQueue queue;
As you're typing RequestQueue, it might autosuggest it, or it might turn red after you type it (I can't remember for sure). If it autosuggests it, just select it, and you're done. If it's red and underlined, press Alt-Enter, and there should be an option for something like "Add from module 'volley'" Select that, and you're done.
(Sorry if this isn't all exact. It's from memory.)