Exit IE and restart, then load important.asp. You should see the contents of that page, not the login page. You'll exit IE a lot, so you may want to make use of setting home pages. Documentation for VBScript is in the MSDN online docs. The examples in this lab will tell you much of what you need to know, anyway.
Session is a global variable that is available as long as the user is on-line.
The If test just checks the flag. We are generating a response to the user in a buffer. If the If test fails, we just go on reading the page. If the test succeeds, we need to flush what we have been generating and send a different file, the login.htm file, instead. Response is a defined object in VBScript.