Multiple websites on one IIS server

IIS specific:

So if I have two domains i.e. domain1.com and domain2.com, both pointing to the exact same IP address (i.e. 1.1.1.1) on port 80.

How do I take users from domain1.com to one site, and users requesting from domain2.com to another site?

Additionally how do I set up subdomains? Someone requesting x.domain1.com should go to a third site.

Many thanks!