As we learned in the Treble Clef & Line and Space Notes post, there are line notes and space notes. Line notes have the line going through the center of the notes. Space notes are found in between the lines. Both line and space notes are found on the staff.
The bass clef space notes are A-C-E-G. The lower the notes on the staff, the farther they are away from middle C.
For more left hand practice, see Bass Clef Practice.