Checking if user is logged in and inputting their username I have a form on my website and i would like the page to check if the user is logged in, if they aren't, then redirect them to a login page, if they are, then show the form.

When they are submitting the form, how can I get that users username and get that review that they submitted show up on their account?

If you need any more details just comment.

I am using Drupal 7
First make sure only users with a specific role can access this form. You can use the #access property to restrict the access to a specific form.
The LoginToboggan module can redirect the user to the login page if they get an access denied.
In the submit hanlder of your form you can access the current user by adding global $user at the top of your method.