It's pretty straightforward, all you have to do is 'like' L'occitane en Provence Australia on Facebook and submit your details for a free 10mL cream voucher (worth $4 apparently) which you can redeem at a L'occitane store.
It's also stated that if they reach 35,000 fans on Facebook by 4/5 that they'll upgrade everyone to a 30mL cream. Our community is big enough - isn't it? ;p
Sounds like what they're going to do is send out a voucher by email and you can redeem it for the product instore.
I suppose it can't hurt to get all your family members with accounts to at least like the page. If you feel bad about claiming multiple gifts you won't have to, you can just disregard the email voucher they send to you :)