Hello and welcome, suruchi.
Free ebooks are easy to find and download, yes.
One of your best sources is right here, in this forum, in the ebooks section. There you will find mainly public domain books formatted by members of the forum, in any format you might wish.
Also, take a look in the freebies section, there are many sites that offer free ebooks, either public domain or self-published ones, or even offers on commercial titles.
You can start by having a look here
https://www.mobileread.com/forums/showthread.php?t=43794