The best way to learn SQL Server 2014 is that which is the best for you.
Some people prefer to buy a book, some people want to study tutorials available on net and some others want to start course(s).
I'd suggest you start here: Tutorials for SQL Server 2012[^], because tutorials for MS SQL Server 2014 are not available at this moment. Sorry, see solution 3 by King_Fisher.
You need to split 2 things:
1) If you want to become a database programmer - learn
SQL[
^] - a structured query language
2) If you want to become a database administrator - learn about managing SQL server
;)