If your organisation already has a web server or hosting service that you
are required to use, then you need to talk to your administrative people to
find out what technologies are supported on that server or hosting service.
There's no point learning ASP.NET only to find that your server supports
only PHP or JSP.
If your server or hosting service supports ASP.NET, or if you are free to
choose the server technologies you want to use, then for Microsoft's
solution check out
www.asp.net
There are non-Microsoft solutions as well, of course, but I don't know
enough about those to suggest any resources.