Auto Fill Text Fields

How do you do the "searching" in the text fields. Like when you start typing something into the text field and it pops up with a drop menu showing you all the results.

How do you do where like you have checkboxes and you click one. It will change the form to whatever you want it to be. Like if I have one that says "User Registration" and another one that says "Writer Registration" it will change the form data underneith the checkboxes. Also when nothing is clicked it will show nothing.

How do you do like what you see in user registration forms when you type in a username and depending on whether the username is available or not it will change between a check or an x for every letter typed.

Sincerely,
Jordan Martin
Seraskier