I don't know what I believe in, either. In fact I think the only thing I really believe is that of course I don't know, the universe is a mystery and I don't presume to be able to understand it. Which means I don't think it's all science either. I think it's unknowable.
But I do know a couple of things for sure. I know my mind/the way that I experience my mind. And I know the things that happen to me. Because I believe that there's a meaning (maybe not a meaning involving a god or souls, but something) then I believe that these things, my mind and my experiences, are the only tangible bit of that meaning that I have contact with.
And there are some things that I reject. I reject the idea of a higher power in the anthropomorphized sense, because my sense of what the meaning must be is that it must be just. We are thirsty, so there's water. We're hungry, so there's food. We're spiritually hungry, too, so there must be a meaning. I don't think that meaning is a creature that performs small interventions for those that are already safe while letting genocide and starvation destroy others. That kind of illogic can't come from a consciousness. There are some truly terrible things in this world and whatever meaning there is will have to encompass all of it.
So that said! The meaning of everything! Way too big. I have no clue. Why am I, a young woman, blessed with my own financial independence and career when women in other parts of the world are treated as property? Too big for me, that is unknowable.
But my mind and my experiences are knowable, or at least fathomable. So I look for the meaning there. It's hard to do this, I have to remind myself all the time. But especially when something is hard, I look at the meaning. What is the lesson? What is the positive side? If this happened for a reason, what would that reason be?
Now I don't know for sure that there is a reason behind everything. But I know that when I look for one, I can usually find one, and finding it usually helps me. So by the end it doesn't really matter if there was an inherent meaning or if life is just chaos... the meaning I find is always valid and can always help me get through.