covalent bonds

Please explain difference between pi and sigma bonds to me. I've been reading chemistry all day long and my brain just can't absorb anything more from books so maybe someone can explain it simpler.

the electron density of pi bonds 'looks' a lot like the greek letter pi... hence the name.  two pis actually opposite each other with sigma electron density between.  the sigma e- density is mostly centered between the two nuclei, allowing free rotation around the bond (the atoms can spin on the axis through the bond/nuclei).  the pi bond, kinda like clamps on either side of the sigma e- prevent the atoms from rotating about the axis of the bond.

or something like that.