Hiii

Please type www.aiimsexams.org and you will be directed to the aiims website.
There you will find a tab named Academic Courses. Click on it and a new page will be on the screen. On this page you will find MBBS written in one coloumn. Click and MBBS and a dialogue box will appear.
Click proceed and you will be directed to a new page where you will have to do the registration. Click on new registration and you will get the application form. Agree to all terms and start to fill the form.

Or simple refer to following link
http://ugcourses.aiimsexams.org/#!
and click on New registration and start to fill the form.

Thanks!