Dear Nabeel, First things first. The eligibility criteria to apply for NEET is that you should be atleast 17 years of age or will turn 17 by December 31st. Your highest educational qualification should be +2 with atleast 50% if you are from general category and 40% if you come under OBC/SC/ST. You should have passed your +2 as a regular student or should be appearing as a regular student. Candidates who are private students and studied in open schools are not eligible for NEET. 

You can fill in the NEET application only online. Please go to NTA website using the link, https://www.nta.ac.in/medicalexam. Click on Register and register yourself with your details. Fill in the application carefully without any errors because not all mistakes can be corrected in the correction window. Once you fill in the form, upload your photo and signature, make the payment and print the page. Do remember the phone no# and email id that you provided because those are the channels through which you will be communicated regarding your admit card and any other such information. I would suggest you to go through this link for detailed information. https://medicine.careers360.com/articles/how-fill-neet-application-form