Kelly,
Jon is right, buying rentals is "investing". If you have little-to-no cash available, you have two options -
1. Build up cash reserves & then invest in rentals. Find amazing deals, lock them up under a contract, and then wholesale them to landlords that actually have cash. You won't be making too much on each deal ($5k-$10k per contract that you sell), but that is dependent on the types of deals that you are able to negotiate. The benefit of this strategy is that you don't have to lay out any money & you learn what is a good deal & what is garbage without any risk.
2. You can follow Jon's advice above. Look for homeowners that need to sell and are willing to offer owner financing, lease options or some other kind of desirable terms. This will take some money though - oftentimes, the homeowner will need to bring their mortgage current or a down payment for some moving money, etc... You'll also have to keep your holding costs in mind. If you can't find a tenant for the property, you will be responsible for the monthly payments.