OK, so I'm assuming you bought a Taurus 24/7 in .40 caliber, right?
Any of the cheap ammo will be fine for practice, but as someone above said, for actual self-defense ammo, you will want a jacketed hollow point bullet (JHP). Gold Dot, Winchester Silvertip, Cor-Bon, Federal Hydra-Shock, Hornady TAP are some good ones. Whatever type you buy, do NOT just buy a box of 20 rounds, load up and think you're good to go. I know these brands are expensive, but you need to make 100% certain that your gun will reliably feed that particular type of ammo. A life-and-death situation isn't the time to find out that your gun doesn't like Gold Dots or whatever brand you go with.
Some people say a couple hundred rounds without any failures is the minimum they'd go with. If that's cost-prohibitive for you, then go with 100 rounds
Even with only 100 rounds, you'll be looking at around $75 for it. Sounds like a lot, but it's worth it to know that when the poop hits the fan you aren't likely to have a misfeed.