and if you accepted it (after negotiations of some sort), you will be given the go signal to do all the formalities in travelling here (I am talking about our country, Philippine). The letter-offer will served as the provisional contract which is a legal document per se in the process of recruitment.

But the formal contract is done here with the stamp of the ministry. If there is a BIG difference between the formal and the letter-offer signed back home, then that is subject (?) for re-negotiation (if one can).