How do Bass Guitars work?

I see that most Bass Guitars are 4-5 strings yet standard guitars have 6 strings

how does that work out? Does a bass-guitarist have to relearn new chords to match the different string number
or do you form the same chords, as with 6-string standard guitars, but leave the bottom(or top) fingers of the chords hanging off?

Do bass-guitars even use chords? Please explain bass-guitars to me!