At wide/large apertures, your photos will have a shallow focus, where only your subject is sharp and the foreground and background are out of focus.
A small f-stop number indicates that the aperture blades in your lens are open fairly wide. So an f-stop of around f/2 or f/2.8 means you are capturing a lot of light. At wide/large apertures, your photos will have a shallow focus, where only your subject is sharp and the foreground and background are out of focus.