将两个asp.net网站合二为一

i am new in asp.net i dont know to how to combine two asp.net web site into one like domain and subdomain concept. i know the procedure to host one web application in local iis. Please explain the how to combine two application and how to host in local iis i.e) single url as domain(one web application) and subdomain(another web application).i am new in asp.net i dont know to how to combi