This website is supposed to be a game where the players have some 'buildings' and these buildings produce resources. E.g. an iron mine may produce 30 pieces of iron ore per minute and automatically add it to the user's inventory. It doesn't matter whether the user is online or not, it should be running 24/7. So when the user does log in to their account, they will see their stack of iron ore has built up depending on how long it has been.
Some pointers in the right direction would be greatly appreciated :)