Once a Free Spins Bonus is available to be used on an eligible game (i.e. it has been accepted), the Free Spins icon will be displayed on its game window. Click the Free Spins icon to open the Free Spins widget; clicking 'Play' in the widget will launch a Free Spins session in a separate window.
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'.