You need a strong grasp of C programming, I'd recommend:

1: Join the Linux kernel mailing list: http://www.tux.org/lkml/

2: Read a book like this: http://www.amazon.com/Programming-4th-Edition-Developers-Library/dp/0321776410/ref=sr_1_sc_4?ie=UTF8&qid=1415153633&sr=8-4-spell&keywords=Crogramming

3: This is a cool site: http://www.learn-c.org/

Cultural immersion is also important, I would find relevant channels on irc.freenode.net and make friends there where you will find amazing free support from the community.

Once you're a little more comfortable in the language I would start trying to read the kernel source code, or maybe try to fix bugs that are posted about any programs that you are interested in learning more about.

For a beginner I'd recommend Programming in C, it's written in a clear and readable way, with useful exercises, and does a great job explaining the basic stuff.

Secondly, Pointers on C is a fantastic second book, and very much underrated. Much more focused around pointers and memory, and integrates that stuff into it's code examples from the start. This book was massively useful to me when I wan learning, but, it can be hard to get a copy for a reasonable price.

If you're not a complete beginner then go for The C programming language .

If you need to get up to speed on both programming and C, then I'd recommend something a bit more friendly such as Programming in C

Programming in C by Stephen G. Kochan

Hands down the best beginner book

A new version (4th) was just released this past August.

Any experienced programmer will tell you so. The K&R book is an excellent resource however Programming in C is much better suited for an absolute beginner.

If you are a total beginner then read C Programming Absolute Beginner's Guide, Third Edition by Greg Perry & Dean Miller
https://www.amazon.co.uk/Programming-Absolute-Beginners-Guide-Guides/dp/0789751984

If you have some basic experience in another language such as Python, Visual Basic, JavaScript, etc. then read Programming in C, Forth Edition by Stephen Kochan
https://www.amazon.co.uk/Programming-Developers-Library-Stephen-Kochan/dp/0321776410

If you are comfortable programming in another language such as Java, C#, Python, etc. then read The C Programming Language, Second Edition by Kernighan & Ritchie (also known as the K&R book)
https://www.amazon.co.uk/C-Programming-Language-2nd/dp/0131103628

Start with finishing this whole book. Start to finish. It is so amazingly helpful: https://www.amazon.com/gp/aw/d/B00EANJ09U/ref=pd_aw_sbs_351_1?ie=UTF8&psc=1&refRID=ZHNDKD9899ZNDSAXDA4V. Even if you aren't an absolute beginner. Then, once you are done with that, read + complete the exercises for this book: https://www.amazon.com/gp/aw/d/0321776410/ref=pd_aw_fbt_14_img_2?ie=UTF8&psc=1&refRID=78FY6PWRFXNDM0DQ2DGW you will literally look back at this post, and laugh at how much more you know after reading these books. I promise.

For pointers, they literally just "point" at that address in memory. The: 1234 cherry st.. That address is actually considered a pointer. Just imagine your computer pointing a finger at that address in its physical memory. Like I could physically point to your house on a map, using the address you give me..

I know that Harvard University uses Programming in C, by Stephen Kochan.

Excellent book: https://www.amazon.com/Programming-C-4th-Developers-Library/dp/0321776410

If I had to restart from the beginning, knowing nothing about computers or programming, that would be mys starting point.

K&R is just not a good programming book for beginners in 2018.

CS50 used to recommend this book to read and do exercises along side online content: Programming in C

One of the best textbooks I ever read.

My General Thought

I find it is best to learn and get exposure from several book/media sources coupled with actual application of things learned.

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Introductory Texts/Links

Short Intro
http://heather.cs.ucdavis.edu/~matloff/unix.html

C Programming: A Modern Approach
http://knking.com/books/c2/index.html

Head First C (Different Presentation Style, check amazon preview)
http://www.amazon.com/Head-First-C-David-Griffiths/dp/1449399916/

Programming in C
http://www.amazon.com/Programming-C-4th-Developers-Library/dp/0321776410/

PDF Tutorial
http://phy.ntnu.edu.tw/~cchen/pdf/ctutor.pdf
Original Here > http://www.tutorialspoint.com/cprogramming/index.htm

C The HardWay (Mostly complete)
http://c.learncodethehardway.org/book/

Zed's K&R Critique
http://c.learncodethehardway.org/book/krcritique.html

Practical C Programming
http://shop.oreilly.com/product/9781565923065.do

Ben Klemens Modeling with Data book has a short C introductory section.
http://ben.klemens.org/pdfs/gsl_stats.pdf

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Reference
Harbison and Steele C Reference Manual
http://www.careferencemanual.com/

Plan on developing on Linux?
The Linux Programming Interface: A Linux and UNIX System Programming Handbook
http://www.amazon.com/dp/1593272200/

Didn't get Pointers?
http://www.amazon.com/dp/1449344186/

21st Century C, This book got dogged a lot, but I think its a nice text.
http://www.amazon.com/21st-Century-Tips-New-School/dp/1449327141

K&R Scan (If you want an idea what's inside K&R)
http://www.iups.org/media/meeting_minutes/C.pdf

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Need an Editor?
VIM Book
ftp://ftp.vim.org/pub/vim/doc/book/vimbook-OPL.pdf

Vim Video Tutorials
http://derekwyatt.org/vim/

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Back in the Day
I used these books years ago. They're somewhat dated, but still useful and cheap.
Programming in ANSI C
http://www.amazon.com/Programming-ANSI-Hayden-Books-library/dp/0672484080
Advanced C: Tips and Techniques (Hayden Books C Library)
http://www.amazon.com/Advanced-Techniques-Hayden-Books-Library/dp/067248417X/

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C Language Basics
How do I read/write files
How things are implemented at a lower level
Compiler Options and Functionality
What is a make file?
Debugging... How to do it... How do I use a standard debugger like GDB?