Admission in engineering colleges happens mainly in two ways:

1. Through JEE Main exam: Most good colleges give seats based on your JEE Main rank. This is called the 80% All India Quota or merit-based admission.

2. Through 12th class marks (20% seats): Some colleges reserve around 20% seats for students based on their 12th board exam marks, called the State Quota or management quota.

So, admission can be either by JEE Main rank or by your 12th percentage, depending on the colleg e rules.