Real estate investing involves the purchase, ownership, management, rental and/or sale of real estate for profit. Improvement of realty property as part of a real estate investment strategy is generally considered to be a sub-specialty of real estate investing called real estate development. Real estate is an asset form with limited liquidity relative to other investments, it is also capital intensive (although capital may be gained through mortgage leverage) and is highly cash flow dependent.
If you invest in rental properties, you become a landlord—so you need to consider if you'll be comfortable in that role. As the landlord, you'll be responsible for things like paying the mortgage, property taxes, and insurance, maintaining the property, finding tenants, and dealing with any problems. Unless you hire a property manager to handle the details, being a landlord is a hands-on investment. Depending on your situation, taking care of the property and the tenants can be a 24/7 job—and one that's not always pleasant.
If you choose your properties and tenants carefully, however, you can lower the risk of having major problems. One way landlords make money is by collecting rent. How much rent you can charge depends on where the rental is located. Still, it can be difficult to determine the best rent because if you charge too much you'll chase tenants away, and if you charge too little you'll leave money on the table. A common strategy is to charge enough rent to cover expenses until the mortgage has been paid, at which time the majority of the rent becomes profit.
The other primary way that landlords make money is through appreciation. If your property appreciates in value, you may be able to sell it at a profit (when the time comes) or borrow against the equity to make your next investment. While real estate does tend to appreciate, there are no guarantees.