How to send activation link for an email address?

Hi all,
I have one site…
If any guest is wanted to register into this site,we provide the registration form to register by submitting the user name,password,email.

Now i want to send a mail to that email to active the user to login to the site…
For that i want help from experts.

Thanking you…

Well… is not so hard: just add two more fields in your database: key (a string) and a flag to check if the account is activated.

when an user register just generate a random string (dajskdahsjdfa) , save it in the database and send an email too with a link like: http://something.com/validate.php?key=dajskdahsjdfa; When user lands on the page with this url just check if is the right key and is yes update the flag (flag is initialy 0, and is used just to check is an account is activated)