Not sure how you got a hold of MAG-10, as it was banned quite a while ago. Yes it's a prohormone. A prohormone is a substance that your body can convert to testosterone, so it's a testosterone precursor. Some prohormones can also be aromatised by the body, which means they'll be partially converted to estrogen, causing female-like side effects, such as swollen nipples.
This is not something you want to happen, which is why people follow PCT (Post Cycle Therapy) using antiestrogen drugs (Nolvadex, Clomid, etc), this also to restore testicular function. That's right, a cycle of prohormones, like steroids, can shut down your body's natural production of testosterone.
Alpha Male is simply a natural testosterone booster; nothing to do with prohormones.
You sound like you are young. If you're under 21, I wouldn't use any prohormones (or test boosters), as your natural supply of testosterone is most likely very high. I wouldn't risk the side effects of prohormones at your age; all you need to do is get a good workout routine from this site, eat A LOT, including many good fats and protein, and sleep 8 hours a night. I can assure you that will pack on the muscle. Simply taking MAG-10 isn't going to do anything for you.
There are far more knowledgeable people around here, and I hope they'll add/correct to what I've said.
Whatever your age may be, don't take any substances without researching them thoroughly. Somebody gaving you a bottle of pills and toling you you'll pack on 10-15 lbs of muscle is not a valid reason to take them.
Take care, and be careful!