GMAT or Graduate Management Admission is a computer adaptive test (CAT) intended to assess certain analytical, writing, quantitative, verbal, and reading skills in written English for use in admission to a graduate management program, such as an MBA, and as you asked here I am telling it is not compulsory in India as there are so many entrance exam for MBA there beside GMAT exam :

GMAT exam Format
GMAT exam consists of four sections: An analytical writing assessment, integrated reasoning, the quantitative section, and the verbal section.

Section Duration in minutes Number of questions
Analytical writing assessment 30 N/A
Integrated reasoning 30 12
Quantitative 75 37
Verbal 75 41

Section 1 – AWA: for the Analytical Writing Assessment, you will be asked to compose two 30-minute essays. The first essay will ask you to analyze a given argument; the second will ask you to analyze a given issue.

Section 2 – Quant: You have 75 minutes to answer 37 multiple-choice quantitative questions that come in two formats. Problem Solving questions (approximately 22 out of the 37 questions) are multiple choice math questions that ask you to solve for a specific value.. Data Sufficiency questions (approximately 15 of the 37 questions) ask you to decide whether or not you are given sufficient information to answer a mathematical question.

Section 3 – Verbal: You have 75 minutes to answer 41 multiple-choice verbal questions in three formats. Sentence Correction questions ask you to choose the most grammatically accurate sentence. Critical Reasoning questions demand that you assess the logic of short arguments. Reading Comprehension involves reading short passages and answering questions based on that particular passage. Each verbal question type comprises approximately one-third of the Verbal section.