Since there are many folks on this forum that are new to using Mathematica/WolframLanguage I'd suggest that each order a copy of Stephen Wolfram's soon-to-be-released (December 7 2015) "An Elementary Introduction to the Wolfram Language":

http://www.amazon.com/Elementary-Introduction-Wolfram-Language/dp/1944183000/

though I haven't read it yet, there is a clear need for a tutorial that helps beginning users "start right" and avoid the many issues that arise by simply diving in without a helping hand to get the basics in place.

Also another excellent book (but which assumes a certain amount of exposure to scientific, engineering and mathematical subjects but no knowledge of Mathematica and very little if any of programming in general) is Paul Wellin's "Programming with Mathematica®: An Introduction", which I have read.

http://www.amazon.com/Programming-Mathematica-Introduction-Paul-Wellin/dp/1107009464/

So, beginners, get a couple of good introductions to Mathematica and dive in to learning the language!