I recommend Scott Manley's tutorials on youtube. Even though many of them are for older versions of KSP, they are still great to get you started. If you are willing to spend a bit, there is a great book that covers a lot of ground in KSP:

http://shop.oreilly.com/product/0636920035138.do

Shameless self-promotion, but together with some friends I wrote a book for O'Reilly Media on KSP!

Amazon: https://www.amazon.com/Kerbal-Players-Guide-Easiest-Program/...

O'Reilly: http://shop.oreilly.com/product/0636920035138.do

Safari: https://www.safaribooksonline.com/library/view/the-kerbal-pl...