Hello
While taking admission at AFMC in MBBS course, the candidate is made to sign a bond that makes it compulsory to work for armed forces after completing the course, for atleast 7 years. The candidate can also choose to work for longer, i. e. permanent commission.
So, the choice is on the candidate, but 7 years minimum is compulsory.
The admissions are conducted by AFMC, Pune. Application forms are released in the third week of June. Admission are based on NEET scores of that year. There are total 150 seats for MBBS course.

Follow this link for more information on AFMC MBBS admissions
https://www.google.com/amp/s/medicine.careers360.com/articles/afmc-mbbs/amp

Good luck