Basically, as the suspension goes up and down, the tires will toe in and out to varying degrees.

In a handling situation, you have one side of the suspension going down, while one side goes up and this creates conflicting toe directions that aren't always exactly in line with the direction the car is pointed. This requires more or less steering wheel input from the driver creating a situation that may or may not feel like it has directional stability. It also creates scrub on the tires which adds heat which wears out the tread and can compromise grip.

There is a range of angles the fixed suspension parts (control arms) operate in that can complement or fight against the angles the movable suspension (steering linkage) operate in. Stock suspended Mopars will always have some degree of bump steer because the lower control arm pivot point is occupied by the torsion bar and the inner tie rod would prefer to be there, so it ends up being too low in its plane of operation. The alternative to correct this is typically to move the outer tie rod to put it in a better angle with the rest of the system.

While bump steer gets a lot of bad press, most drivers aren't capable of really noticing it unless the set up is really, really bad.