Gmail gives users the ability to invite friends to sign up for Gmail accounts. If you don't happen to see a blue 'Invite a friend' box in your account, please be patient -- Gmail invitations are always randomly distributed.
If you have the ability to invite friends to try out Gmail, you'll see the 'Invite a friend' box on the left side of your Gmail account. Just enter your friend's email address in the text box, and click 'Send Invite' to instantly send an invitation. If the person you're sending an invitation to is in your Contacts list, Gmail will auto-complete his or her email address for you. And finally, if you'd like to look at the invitation you're about to send, click 'preview invite.' While previewing the invite, you can also personalize the message that will be sent to your friend.

If you should run out of invitations, you'll no longer see the option to invite more friends to create Gmail accounts. For now, we can't give you more invites, even if you ask nicely or offer to tattoo Gmail on some part of your body. (You'd be amazed at what people will offer for a Gmail invitation.) Gmail may, however, randomly grant invitations to your account as they become available in the future.