Here is a basic wiring diagram for a multi tap 250w M58/M37 magnetic ballast which is exactly what I have. Its really easy to wire. My 120v incoming line (black wire on my cord that comes from the wall outlet) goes to the blk/yellow wire coming out of the ballast. The 208v taps and up are not used on my multi tap since my ballast is running on 120v so those are tied together and not used.
Second, the red wire coming out of the ballast connects to the capacitor. Third, the other half of the capacitor is attached to the middle connector of the bulb socket. Fourth, the outside connector of the socket is attached to the common (yellow) wire. Lastly, the neutral wire (white) coming out of my power cord is attached to the common yellow wire coming out of the ballast.
It may look a little complicated, but once everything is in front of you, you will figure it out.