Stool softener (Colace = Docuasate). It’s job is to go into your digestive tract and attract water to soften things up.
Laxative (Dulcolax = Bisocodyl) = intestines tickler. Increases peristalsis (natural, rhythmic wave-like movement of your intestinal muscles).
Constipation can be caused by either that rhythm slowing down or stuff being so hard that the natural rhythm can’t move it fast enough.
Stool softeners make things softer so the natural motion can move it out, laxatives make the natural wave motion wave faster.
The downside to a stool softener is that it might not work fast enough for some people.
The downside to laxatives is that they might cause cramping and pain, and actually lead to diarrhea.