To take part in Stars Freerolls, all you need to do is finish in the top 27 of a 'Satellite Stars Freeroll' on PokerStars.fr. These daily qualifiers are free to play and run daily at 20:00. You will find them in the client lobby under 'Tourney' > 'Satellite' > 'All'.
PokerStars, GGpoker, and partypoker are an example of the sites that have these freeroll steps on offer. The lowest step is free to enter. Win that one, and you'll find yourself with a ticket for Step 2. Continue on and you could make your way to a hefty payday, all for free.