I have a 1982 Chevy K20 pickup with a 350 and a coil in the cap HEI distributer.

THe distrubetr is in but I cant figure out what wires plug into the distributer for the coil. There are 2 prongs one sideways and one normal. What plugs in here?? I cant find a wire with the 2 prong setup that matches . Does it really only need a one prong plug? Also just for reference what is the plug that plugs into the coil? WHere does that wire go and what does it do?