End Effector is WHERE you want to move the foot TO, Joint Location is where the knee/elbow should be (so that the solver knows which way to bend the bones, otherwise it might try to bend the thigh backward and the shin forward to reach the same space), IK bone is the actual bone to start solving from (i.e. the bone you want to move to the End Effector location).
As for setting them up, you need to store the hits of your downward traces (that determine the ground below the feet) as variables, then feed those variables to the End Effector location in world space.
The joint target should be set to 0,0,0 in bone space, with the bone name being the name of your IK knee pit bone (assuming your rig uses an IK knee pit setup rather than an FK setup that just follows the bones down)
The IKBone should either be your shin or foot, depending on how far up the two bone IK actually solves (I’m not entirely sure).