I'd suggest not breeding anything, to be honest. I've bred fish for years and a) it's a lot harder than it looks if you want something other than guppies and b) you'll need equipment like a bubble wall, food, probably a brine shrimp cultivating kit, aquarium salt, disease treatments, microscopes are useful... the list goes on. If money isn't something you have right now, breeding probably isn't the way to go.
While guppies are easy to breed and tend to do it of their own accord, you can't stop them and you'll get overrun within a few months. They're hard to sex when they're babies and in my experience, they were already sexually mature (and pregnant) by the time I could tell them apart. I bought one female guppy and within about 6 months, I had over 300. You'll definitely need a bigger tank for that!