davo is right, was different for me tho since i didnt buy directly from the devs.

You only get one username and password and you use this to unlock the game. I wouldn't share these details with anyone because they're likely to steal your account. The onyl way to unlock is to use these details. You can unlock as many times as you like. However you only get an extra unlock every week. So after your first 3 are used up, you only get 1 every week after that. Use your unlocks wisely, account sharing is frowned upon unless in the same household.

Yep, the unlocks are issued directly into the user account that has purchased the game.

You will have 3 unlocks which you get a 'free' unlock at the start of every month (not week) to a maximum of 2 or 3 again.

If you require anymore than that you will have to contact the devs and beg for one (aslong as it is not excessive you are generally sent another unlock)

I beleive you can use these unlocks to unlock your account on more than one PC, but as Davo says they are for yuor OWN use not sharing.

There are several threads about this subject that contain more information, if you use the search tool above you will be able to find them easily