From where can I download programming/coding or any book related to computer science. I am trying to have a collection of epub/mobi/azw3 programming/computer science books. Is there any site for that or can anyone share me those ? I don't want pdf because they are almost impossible to read on kindle.
Depends on a lot of things.
First, are you using an eink version of a kindle? or a Kindle Fire?
If you are using e-ink (and therefore can't use pdf easily), I would recommend buying ebooks from Oreilly or Packt Publishing. They're very expensive, but at least they will format properly for an eink device.
(by the way, both companies have pretty good sales (and occasional free downloads), so I would recommend signing up for their email list.
If you have a Kindle Fire, then all you need to do is to download a PDF reader app (there are many -- don't try to read things with the Kindle app).
You may be limited by what you can afford, but because PDFs are not reflowable, you want to get a fairly good screen size to read them. You need at least 8 inch screen in my opinion. If you buy smaller, the text size will be hard to read. (There's a zoom function in smaller devices, but it's inconvenient).
Try http://openbookproject.net/thinkcs/ for a good (and famous) introduction to basic structures (using python as an example). I recommend this for starting out. Here's the pdf of the latest version http://www.ict.ru.ac.za/Resources/cspw/thinkcspy3/
(Older editions of this book in other computer languages are here: http://www.openbookproject.net/thinkcs/archive/ ).
Here's a list of ebooks for free out there https://github.com/vhf/free-programming-books/blob/master/free-programming-books.md
One more thing. If you have kindle fire, I would sign up for evernote, download the app on your tablet and then clip recent web tutorials on subjects which interest you. this is a good way to read articles when offline; evernote renders the content pretty well.
Finally, I want to really recommend buying a tablet which you can be comfortable reading PDFs on. 6 or 7 inch tablets just aren't good enough for most people to read PDFs on. I have an ipad 1 with the 10 inch screen and I still use it for reading technical manuals.