A great website to learn about off camera flash is http://www.strobist.com . It’s free content and I’d recommend it to any photographer. It has a great “lighting 101” tutorial that walks you through what to buy and how to use it in a very understandable way. The gear itself will probably run you around $100 on Amazon, a cheap hotshoe flash, a stand, an umbrella, and a sync cord.
Your work looks very promising, a few things we could nitpick but overall very good. Keep it up! 🙂