#3
It means you raise the third to a perfect fourth or lower it to a major second.

C chord: C E G
Csus4: C F G
Csus2: C D G

Often, a sus4 chord will resolve to a major chord (Csus4 to C) and sus2's will resolve to a minor chord (Csus2 to Cm) but this is hardly a definate rule. However, it is a much of a rule as it can be that a sus chord must resolve to some other chord.
#4
'sus' means suspended in case you weren't sure.

...and cos there is no 3rd, they cannot be classed as maj or min...which is kinda cool.
#5
Yeah, 'sus' stands for suspended, and it is replacing the major or minor third with either a major second or a perfect fourth; as with most chords, these also have their own unique sound.