Perhaps one of the biggest rites of passage for a photographer is gaining proficiency with artificial light. It can seem a bit daunting at first, but once you get some basic principles down, it's really not that hard, and you'll greatly expand your photographic capabilities in the process. Dive into this great video to get started.
Coming to you from Mango Street, this video will help you transition from natural light to strobes. As they mention, you don't need an ultra-expensive kit to get started; grab yourself a cheap monolight kit to learn with. You can always move up to more expensive sets in the future, but for the purposes of learning how light behaves and nailing down those basic principles, any old kit will do. Be sure to pay attention to how the size of the source and the distance to the subject affect the light quality. Second, Daniel DeArco makes a great point about paying attention to the quality of the natural light as you add in artificial light to supplement it. Be sure to match them appropriately (unless you're going for a certain look). Finally, experiment, then experiment some more! You can read about lighting all day, but at a certain point, you just need to do it to get a better instinct for it. Go out and shoot!