I've only been to Paris a couple of times, but to put your mind at rest, Paris is best explored on foot. The actual city (where you'll be staying) is small and compact and this is where you'll find the Eiffel Tower, the Louvre, Montmartre, Notre Dame etc. If it's your first trip, then just explore the city centre, but if you get the time I recommend visiting Versailles which is in the Paris suburbs and you can get to on the subway very easily.
One of the best introductions to Paris is to take a boat trip along the River Seine, which divides the city in two areas, known as the Right and Left Bank.

Best thing to do is get yourself 'Essential Paris' published by the AA for about a fiver - should be able to find it in most Waterstones etc. Gives you very simple information about where to eat / stay / visit and it isn't too overwhelming. Let us know if you need to know anything else :-)