A stave is normally five lines on which music is written. Sometimes where pitch is not necessary, percussion for example, the stave can be just one line to allow the rhythm to be written.
Music can be written above and below the stave by many notes using ledger lines rather like a ladder to extend the stave.
A clef allows for the definition of pitch on the stave. The two common clefs are the treble and bass. These are used together in piano music to form a great stave. The note Middle C is on a ledger line which sits between the two clefs.
Different instruments use different clefs for example a cello will use the bass clef and the oboe will use the treble. When the clefs are used on their own, i.e. music written for the oboe will just use the treble clef, Middle C will be at the bottom of the stave. For the Cello in the Bass clef, it will appear at the top.
Below are the common clefs showing the position of Middle C. For an instrument or voice using the treble clef, the note Middle C is a low note. For the Bass clef, it is a high note. This gives you some of idea of what instrument or voice would use each clef.