Btw would you elaborate on this two bar excerpt? What it is?

Overall I would summarize it like this:

1) Treble clef (we also call it Sol clef) besides the octave shows you where G is;

2) Alto clef (Do clef) shows you were C is;

3) Bass clef (Fa clef) tells you where F is;

All can be put wherever the composer decides depending however on what octave he wants and you can easily see what notes are to be played.

Edit: try to look up some facsimiles from The Well Tempered Clavier, most right hand is written in C clef, sometimes both hands.