Hi student,

NCERT's books are the foundation stones of UPSC preparation. As COVID-19 is spreading, you should download the books from the NCERT's official website. To download the E-books from NCERT's official site refer here - http://ncert.nic.in/textbook/textbook.htm

Select the class, subject as well as title of the book to download it.

Feel free to ask doubts in the Comment Section.

I hope this information helps you.

Good Luck!