Shortcut to finding files on your computer?

I didn't really know what to call this.. But when you're looking for a file to select on your computer, you usually type in a few letters and then your computer kinda guesses to what you could want to click. This is turned on by default, but I think someone turned it off and I don't know how to put it back on. Like say you're looking for a picture and its called "flower" or something. when you type in like "flo" "flower" and other picture names with "flo" in them should show up. How do I get this back?