How. Just. How.

I can't understand how everyone can do it. How can anyone smile and laugh like that, how can anyone still want to live knowing all the awful things that happen, that will happen? How can they be so happy, so carefree? How do they walk through each day, seemingly so normal, so cheerful? I watch them, and I wonder how they do it. I could never do that. I can't smile without it being fake, I can't laugh without it being a hoax. I don't know how to love people, I can't feel emotional attachment. How do they do it, loving and living? I wish someone could teach me these things. I wish I wasn't like this, I don't want to be suicidal or depressed. I want to be able to smile like that, to be able to not worry about the future. Is there still any hope for me, or am I just too far gone? Is it too late for me to learn how to be happy? Someone please tell me...