Well to post an introduction all you need to do is do the exact same thing you have done here but post in the introductions section. So, post an introduction in the
Introductions forum

and to complete your profile, click on
My Controls, which is located near the top right of the page. From
My Controls, click on
Edit Profile Information which is found on the left hand pane of the screen. Now update your profile and then you done

!
Regards,
David.