Hi MaryJ, Le Mans circuit is a little out of the town so getting there is a bit tricky. The circuit has a little village of its own with food and trade stands so there is lots to see. The museum is also next to the station and is worth a look. There are also busses that take you out to Mulsanne, Arnage etc. and they are worth getting on as well.
Also take a wander round some of the campsites (Maison Blanche - home to many CA's) is close by - it's worth a look at some of the set ups - if you look for the Drinking for Holland guys (you can't really miss them!) you'll find quite a lot of CA's near by.
Hope you have a good time and a good trip