Assuming you're in the U.S., I highly recommend taking a Traffic Skills course given by a League of American Bicyclists instructor. (www.bikeleague.org) Check the website to find any scheduled in your area.

Next, check your DMV for any bicycling tips. PA has a very nice booklet describing how bicyclists should behave on the roads.

Finally, find a quieter road where you can practice on the weekends. Riding with cars can be a bit nerve-wracking at first, but the fear disappears as your confidence builds.

The best way to ride your bike on the road is to pretend you're a slow-moving car. Stay to the right when it's safe, but don't be afraid to merge into traffic when needed (avoiding obstacles, turning left, lane too narrow for safe passing, etc.).

Don't worry about your speed. Ride at a pace that is comfortable for you.