Here is a basic list of things to understand:
How to Understand Soccer Strategy: 10 Steps - wikiHow
I never understood soccer in my life either, but what makes FM so unbelievable is that you can read articles and watch videos, learning the game, and then apply it to FM, and it makes sense, and works as it would in real life. I had no interest in learning the game until FM came along. It got me hooked on what amounts to "FM crack".