The chromatic circle is a visual that represents what happens when you move up or down the keyboard/fretboard.
For example, if you play a C and move up one key/fret, that would be C♯/D♭. If you play C and move down one key/fret, that's B.
You can use the wheel to identify any note on the keyboard/fretboard as long as you know the one you're starting on. If you move up the keyboard/fretboard, each note or fret is one step clockwise around the wheel. If you move down the keyboard/fretboard, each note/fret is one step counterclockwise around the wheel.
Click here for a PDF version of the circle and the key/fretboard maps.