coding a membership trial period

Question

Hello,
I have an web application that I am working on, and am new to software development.  I have used the WAT and Login tools to establish security on a couple of folders.  I have this working, and am developing the next step.  I would like to set up a 14 day free trial for new users.  Upon expiration, I plan to send them to a payment gateway that will charge a small fee to continue membership.  I have never programmed something like this before, so please forgive me for my lack of programming know-how.  I have searched the major search engines and other discussion boards to no avail.  If I could find someone to help walk me through this, I would be eternally grateful
I have read a few chapters in various books, and watched several videos, but none provide me with an example of which I can model and follow.  I have put together a few lines of code, that don't work, however it is a start.  Here is what I have:
protected void Login1_Authenticate(object sender, AuthenticateEventArgs e)
{
bool validUser;
Membership.GetUser(validUser);
if (validUser < 14)
continue Membership.GetUser();
else(validUser >= 14)
MessageBox.Show("Your trial membership has expired.");
Response.Redirect(Http://www.paypal.com);
}