If you are just purchasing moneypak to use in purchasing btc there really isn't much you need to know. With moneypak you just need to go to any participating retailer and purchase grab a moneypak, take it to the cashier and give them the amount you want to load. The retailer usually charges about $4.95 for the moneypak plus whatever you are putting on it. From there, assuming you have a trade lined up, you contact your exhanger and give them the moneypak number. They use the moneypak to either load a pre-paid card of theirs or load their paypal; once transferred they send you the coins to your wallet. But research anyone you are doing business with because they could potentially take your money and send the coins.