Don't assume that they're familiar with Web forms. Your credit card will be charged. Of course, the name of the game is getting people to click that Big Button, so make it easy for them. Avoid superfluous pages - the fewer clicks it takes to place the order, the more orders you'll get. And display plenty of reassuring messages about the security of your order form.
Some sites go so far as to include a FAQ about credit card security.
One of the best confidence-builders of all is simply to put your company's complete street address and phone number right on the ordering page. Only the page with the actual order form needs to be SSL-enabled. Setting up SSL is pretty simple, and your ISP can give you the details. The technical details of SSL are far beyond our scope here. All you need to know is that although it's possible for a crook to crack an SSL transaction, it would be so difficult that it wouldn't be worth the time and effort to steal a few thousand bucks.