What should I look into to accomplish this.
When you select an input field some text to the right shows up.
For example: https://twitter.com/signup
Anyway i need something like that works with PHP. What should I look in to?
And also How can you query the database and not have to reload the page to see result? For example i have seen on many sites registration you can check if the a username is used without the page reloading. Dont know how to explain better.
You can however, call a PHP script dynamically (to check if a username is registered) using a technique called AJAX.