What should I do to prepare my website
for https. (Do I need to alter the
code / Config)
You should keep best practices for secure coding in mind (here is a good intro: http://www.owasp.org/index.php/Secure_Coding_Principles ), otherwise all you need is a correctly set up SSL certificate.
Is SSL and https one and the same..
Pretty much, yes.
Do I need to apply with someone to get
some license or something.
You can buy an SSL certificate from a certificate authority or use a self-signed certificate. The ones you can purchase vary wildly in price – from $10 to hundreds of dollars a year. You would need one of those if you set up an online shop, for example. Self-signed certificates are a viable option for an internal application. You can also use one of those for development. Here’s a good tutorial on how to set up a self-signed certificate for IIS: Enabling SSL on IIS 7.0 Using Self-Signed Certificates
Do I need to make all my pages secured
or only the login page..
Use HTTPS for everything, not just the initial user login. It’s not going to be too much of an overhead and it will mean the data that the users send/receive from your remotely hosted application cannot be read by outside parties if it is intercepted. Even Gmail now turns on HTTPS by default.