I work with someone like this, who said, "I don't know what I believe, but I go to church every week. And that's something."
It is something, it is a start of sorts. But there could be so much more.
At the other end of the spectrum are those who know deeply that He exists and fear that fact so much that they speak disparaging things about Him, publicly. This is often confused, inconsistant or false theology, misconceptions that come from never actually reading His word.
This would be your Bill Maher, Richard Dawkins, Amazing Atheist types. They don't believe that He isn't real, they hate God precisely because He exists.
In the middle of these two extremes falls everyone who knows a little about Him - maybe what they've been told by someone else, maybe from their own intuitions - and so ventures out in their own way, mostly determined by what they're comfortable with. Some might participate in social welfare activities, some might read their Bibles and pray diligently on their own and never go to church. Others might be very active in church but don't speak of Him outside of it.
But everybody knows that He is there and cannot be denied. The agnostic says he's not sure who God is, but that is only because he's never taken the time to try to know Him. Even the atheist's behaviors are motivated by a hatred of God, not a true denial of His existence. Or, they know how much they need Him, and so they hate Him because they think He doesn't exist.
"If there were no God, there would be no Atheists."