How do people smile?

16 male high school student. I transferred from homeschool to public school about 2 weeks ago and since then I’ve been completely miserable. My entire life has been miserable and I always told myself “when I get out of homeschool I’ll be able to make it,” but that’s just not how life works. Since I got here all I’ve been able to do (besides frown and accept reality) is question “how does anyone smile?” This isn’t a metaphor, this isn’t me being dramatic, I genuinely just want to know why people smile. Do they have someone they care about? Are they excited about their work? Are they seriously fulfilled and happy living in the same world I’m living in right now? Every time I see someone smile I get an urge to go up to them and choke them out until they tell me what they’re so fucking happy about. So please, please tell me why people smile because I can’t figure it out.