They can be understood as an equivalent of the pre-public examination that colleges conduct.
Getting through the end exam (i.e. equivalent of pre-public) is compulsory for the institutes examination.
Oral CoachingThe coaching process involves conduct of examinations (eligibility tests) at the end of the coaching period.
A student will be made eligible to appear at the main examinations only if he qualifies in the end examinations conducted by the oral coaching center that he/she joins.
Postal CoachingThe student is supplied with a set of a set of question papers along with the study material in each subject. The total study material is divided into parts and the question papers would be such that a student would be able to answer the first set after studying a part of the material from the beginning.
The answers to the question papers provided with the study material are to be periodically submitted within the time limits prescribed. The submitted answer papers would be evaluated and returned to the students. A student has to qualify in the required number of papers within prescribed time limits, to be eligible for appearing at the main examination.
This amounts to doing a correspondence course, attending the pre-public examination at home and sending the answer papers for evaluation to the institute.