In a 4K gallon pool, each cup of 6% bleach should raise your FC by 1 ppm. With a CYA of 50, you need to keep your chlorine levels between 3 and 6 ppm at all times, so that should help you figure out how much to add. When adding it, you can either pour it in the skimmer, assuming you have no other chlorine source like trichlor or cal-hypo in the skimmer, or you can add it into the return stream, pouring slowly so you don't splash it on you, your clothes, or your liner. You can walk around the perimeter of the pool and pour it in, too, being careful not to splash it--just use a broom, net, or other equiment to help stir the water up after you add it.

Once you add the bleach, no need to wait to swim--just make sure it's well mixed into the water, and go! (That's why I put mine into the return stream--it helps dissipate it faster). Might want to make sure eyes are closed underwater for a bit, just in case...