FIFA 13 is definitely the most complex FIFA game to be released so far. Defense is a very difficult thing to explain if you don't understand the basics of Association Football. My best tip would be to do some research on "soccer" to find out how the game is played and what the standard formations stand for, and what formation does well against other formations. Just to put it simply if you have more players near your goal it's a defensive set-up, if you have more players towards their goal it's an offensive set-up. So if you want to defend, start with a set-up that gives you 5 players near your goal.
A celebration is performed after you score a goal. I'll add a good link for how to do them at the bottom of this. A last good tip would be to take your time. If you rush into the goal and try to quickly score, and you're playing against someone who is not the computer on very easy, you will lose the ball. Take your time and learn to dribble the ball. Aside from that, practice practice practice.
You play ranked matches through the Ultimate Team section (I think it's called that, it's been a month or so since I played it, Halo 4 came out). Just choose ranked. Hope that answers your questions!
The celebrations link: