You'll need to download a fairly big file before you can start playing.
There have been 2 expansions since the original release of the game, and I believe you can get a 10 day trial of each of those giving you a full month of free play time, and then another free month upon purchasing the game. That's how I got into it anyways. Come to think of it, it was a year today that I started playing. As Coarzu said starting out is pretty overwhelming.
If you wish to keep playing you can purchase the game from the WOW site and download it, or you can buy it from any store that sells computer games. If you buy it from a store, downloading a bunch of updates will still be necessary.
If you PM me your email address I can send you a link to the free trial. ( if you end up purchasing an account I will receive free play time)
Otherwise click
https://signup.worldofwarcraft.com/trial/index.html
have fun