Imagine, once upon a time, someone used eleven lines, ten spaces, to represent mostly the notes that could be sung. It would work, but got quite confusing. Inventor B had a better idea. "Let's get rid of the middle line1" A replied "But we need it for notes on middle C" B then says "True, but if we leave that line out, it can always go back smaller if and when middle C notes are played."
So, we have the two lots of 5 lines, and a little ledger line for when C needs it. When there's notes below that that need to be written when there's only a treble clef available, then the next two or three lines down - those that usually belong to the bass clef - are used as well. Guitarists are used to seeing a note in the space below three ledger lines - it's their bottom E.
It would be a pain when writing for the bottom strings of a guitar to suddenly find you had to write it in bass clef. And it's the same the other way, at the top of the treble clef. There's a way around that, though, using '8va' or 15va'.
And, no, the two C notes quoted are not the same - they're an octave apart.