There are several ways, and actually the same as you have probably been using in ASP.
1. You can use the URL (querystring), e.g. default.aspx?variable01=10&var02=something
2. You can use a Session object to store variables in. You can get much more information on the use my searching either this forum or using Google.
3. You can also use hidden fields in forms if you are posting a form.
4. Probably something I have forgotten ;)
Hope it helps,