[Cubbies87]

As far as the rules go, find out what rules the league you will be umpiring for is using. If it is FED rules, get yourself the FED books, including the rule books, case books, etc. If there are special exceptions to a widely published form of rules, obtain those differences. Then, read through all of them thoroughly twice. After that, read one page a night, and make sure you really understand everything written on that page. You'll catch on pretty quick using that method.

Just reiterating what everyone else said with experience. Everything gets easier over time. As far as the mechanics go, find a reliable source, either human or material, and learn, then practice the mechanics. They'll become second nature if you practice enough.

Equipment wise, be confident in what you buy. If you're doing lower level, chances are you don't need to spend as much. However, make sure you spend enough that you are confident to take the full force of a wild pitch or a foul ball. If that means you are buying the top of the line equipment for a 9 and under league, while you may be a bit of a wuss, it's better than being afraid. There are zillions of online retailers, many of which send out catalouges free of cost. Run an online search, and ask around.