There are many threads in the tank forums that go over tank mechanics.
Checkout the link below and read through the thread. Also note the post in it on the first page that links to other tank advice threads. Reading through those should give you a general idea.

http://forum.square-enix.com/ffxiv/t...irst-time-tank

As for specific fights and content, you can usually find guides on youtube that go over the mechanics.