How to make a bassline to fit with guitar riffs?

i know a bass is a rhythm instrument, and should play with the drums, and the bass obv iously doesnt always follow the guitar, but how does this work? ive heard to play something within the chord of what the guitar is playing but also with the drums rhythm. but how exactly do I play with the drums? and when playing with what ever chord the guitarist plays, do i just play random notes within that chord and rhythm with the drums? im so confused