how to activate the activation by mail

I need to know what I must do for activate the system activation by mail?, because right now is off, because I can access without activate my new user.

rigth now Im using the example3.php

I recived the email, but i can access with out activate.

thank you,

Alejandro.

by the way great script, first I was trying with example2.php, but I dont know what's happend, never works fine for me, its register a new user fine, but I could never log in, maybe you i can check if anything is wrong with the script, because I was ready to give up, with your script, so I was looking for another script, but I wanted to try one last time with Example3, becuase i was think that could be diferent and maybe works, and this worked well for me. this can this happen to many people and finally, and many of them could give up and search for another script.