Dear student,
You can opt for IAF in the following ways-

Number 1: Direct entry through NCC.(PERMANENT COMMISSION)
If there is Air NCC in your college, you can join it and try to get a 'C' Certificate.
If you get one, you'll be eligible for direct entry and you'll go direct for your SSB. No written exams.
Also you'll have get a great exposure there and you will also get a chance to fly in the cockpit .

Number 2: CDS Exam(PERMANENT)

After completing your graduation or in the final year you can apply for CDS, clear it, give your SSB, then medicals, You know the rest right!

Number 3: AFCAT(Short Service Commission)

After doing your graduation you can give AFCAT(Air Force Common Aptitude Test) and the rest remains the same as CDS.