suggest useful apps and websites for study material and some notes and resources for mba entrance exam??

For Management entrance exams you can check out the website of Mindworkzz, by Arun Sharma. You can get free video lectures for preparation for CAT, XAT, IIFT and others. They also contain some reading material. You can also avail the benefits of mock tests by paying an amount of 500. Apart from that there are various comprehensive programs for CAT which costs 34700. You can also purchase their books from the website.

Apart from that Career Launcher also provides online coaching for which they charge 60000. But you get a holistic view of the entire syllabus.

TIME provides a regular program for distance learning  for CAT which costs nearly 11000.

Apart from these you can buy books of Arun Sharma and Sarvesh Verma for quantitative aptitude and Arihant's book for logical reasoning. For English you can read TOI which is freely available on their website. You can also go through some articles from Arts and Letters Daily. This will help you to improve your reading ability. And for Data Interpretation previous year questions would suffice. You can also go through some YouTube videos from Testbook which can help you to brush up your basic concepts. For better preparation you can purchase a mock test series from various Institutes like TIME, Career Launcher or IMS which will cost you not more than 15000.

Good Luck