Hey,
CAT or Common Aptitude Test consists of various sections like Verbal Ability,Reading Comprehension,Data interpretation and Logical Reasoning,Quantitative Aptitude. Total number of Questions is 100 and total marks is 300.
First off,be thorough with the syllabus and solve previous years papers and join online mock tests.
You can offer books like:
Verbal Ability and Reading Comprehension:
1.Verbal Ability and Reading Comprehension by Arun Sharma and Meenakshi Upadhyay(Arihant)
2.  English Grammar and Composition by Wren and Martin
3. PSC for VA for CAT by Nishit Sinha
Data Interpretation and Logical Reasoning:
1.CAT 2018 Data Interpretation & Logical Reasoning by Gautam Puri
2.Logical Reasoning and Data Interpretation for the CAT by Nishit K. Sinha
3.How to Prepare for Data Interpretation for CAT
Arun Sharma
For Quanitative Aptitude:
1.NCERT Mathematics Books (Class 6 to 10)
2. How to Prepare for Quantitative Aptitude for the CAT by Arun Sharma
3. Quantitative Aptitude Quantum CAT by Sarvesh Sharma
Apart from that,you should newspapers like The Hindu,The Times of India to build your vocabulary and improve your current affairs.
Hope this helps.
Good luck.

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