What's the best book on gravitation? Also how can I learn tensor analysis?
*Book Gravitation*
One of the most well-regarded books on gravitation is Gravitation by Charles W. Misner, Kip S. Thorne, and John Archibald Wheeler. This book provides a thorough and rigorous treatment of general relativity, the theory of gravitation developed by Albert Einstein. It covers topics such as the equivalence principle, the geodesic equation, black holes, and cosmology, and includes detailed discussions of mathematical concepts such as tensors, differential geometry, and variational principles.
The book is often praised for its clear and concise writing style, as well as its comprehensive coverage of the subject. It is aimed at advanced undergraduate and graduate students in physics, as well as researchers and professionals in the field.
One advantage of Gravitation over other books on the subject is its emphasis on the geometric nature of general relativity. The authors use the mathematical tools of differential geometry to provide a clear and intuitive understanding of the theory, which can be helpful for students who are new to the subject. In addition, the book includes numerous diagrams and illustrations that help to explain complex concepts.
Other well-regarded books on gravitation include The Large Scale Structure of Space-Time by Stephen Hawking and George F.R. Ellis, and General Relativity by Robert M. Wald. The Large Scale Structure of Space-Time is known for its detailed treatment of the mathematical foundations of general relativity, while General Relativity provides a more concise and accessible introduction to the subject.
The best book on gravitation will depend on the reader's background and level of experience with the subject. Gravitation is an excellent choice for advanced students and professionals in the field, while The Large Scale Structure of Space-Time and General Relativity may be more appropriate for those who are new to the subject

The two topics don't appear to be related, but

* Learn Tensor Analysis*
Textbooks: Consider using textbooks, such as:
 A First Course in Tensor Analysis by J.C. Burkill, 
Tensor Analysis: Theory and Applications by I.S. Sokolnikoff, or
 Introduction to Tensor Analysis and the Calculus of Moving Surfaces by Pavel Grinfeld. 
These books cover tensor analysis from *introductory to advanced levels.*

Online Courses: Look for online courses that cover tensor analysis. For example:
*MIT offers a free online course* called Introduction to Tensor Calculus that covers the basics of tensor analysis.
Nasa has a good pdf: An Introduction to Tensors for Students
of Physics and Engineering by Joseph C. Kolecki

Videos: Find videos on platforms like 
*YouTube* Skillshare Brilliant etc. That explain tensor analysis in an accessible way. Some popular ones include
 A Gentle Introduction to Tensors by Grant Sanderson and 
Tensor Calculus for Physics by Physics Videos by Eugene Khutoryansky.

Practice Problems: To test your understanding of tensor analysis, look for practice problems with solutions in textbooks or online resources.
What is 9 + 10?
9 + 10 is 19.
That is the correct answer, thank you.