There are top six popular MBA exam to get into premier B-Schools in India.

1. Common Admission Test (CAT)

2. Xavier’s Aptitude Test (XAT)

3. Symbiosis National Aptitude (SNAP)

4. Indian Institute of Foreign Trade(IIFT)

5. Narsee Monjee Management Aptitude Test (NMAT)

6. Common Management Aptitude Test, (CMAT)

 Also a minimum aggregate score of 50% (45% in the case of the candidate belonging to reserved categories) in his/her graduation or degree exam from a recognized university is eligible for an MBA degree. And final year students awaiting their results are also eligible.

Hope it helps.

Since you are in entrance phase of 4th year so generally  you can apply when you are in last semester of your gradutaion degree.As the minimum elgibility criteria you have to follow is graduation degree with the min. percentage marks decided by various MBA examinations board. 

For eg. 

for CAT the minimum elgibility criteria is 50percent of marks in bachelor degree. So you can only apply in the last semester.

You will have to apply for exams from august-september month the forms start. For that you should start preparing for it. Some of the entrances are like CAT, XAT, CMAT, NMAT etc..

You should have minimum 50% in your graduation.

All the best!