Hi Skorpio,
The camping ticket will (if they are like previous years) have a 4-colour patch on it - approaching LM follow the signs for the colour that hasn't been crossed out.
The campsites are (in the main) on public roads (although the gendarmerie usually put up road blocks in random places!) so you only need the camping ticket to get to BSR campsite.
If you haven't pre-ordered them, your race ticket can be bought from any entrance into the track areas themselves. There's numerous entrances (all of which a fair way from BSR unfortunately - I'm on the same campsite!).
You need to pick up a 'contramarque' (pass-out ticket) whenever leaving a trackside area. You then hand this in again when you go back to the action.