This is something you say when you're giving someone advice on how to do something well. When you think that the key to success is just one thing, you say "it's all about ___". For example, when talking about career success, people often say:
It's all about connections.
This means that being successful in your career is mainly a result of knowing the right people. By the way, there's another version of this phrase with a similar meaning but which is more casual and sounds more negative:
It's all about who you know.
And for one more example, when giving someone advice on hitting a baseball, you can say:
It's all about keeping your eye on the ball.
This means that watching the ball carefully is the most important aspect of hitting it.