Autism

Ugh, being the outcast at school.... I'm sorry you're going through this, but rest assured you're not alone.

There are heaps of unspoken social rules, especially at schools and even more so in your teens. Personally I think that's the most difficult phase of life socially, and being neurodivergent just amplifies that.

It takes time to find people you can get along with. I would recommend looking for any group activities that involve something you're interested in - often it is easier to meet and start to get to know someone when you're doing something together.

Some other thoughts:

• Most conversations start with some kind of greeting and courtesy "how are you". This is rarely a real question; it's basically the social equivalent of a TCP handshake (if you're into IT) for establishing communication. They're expecting a very short, brief answer without details (e.g. "Yeah, not bad", "Doing great", "Ugh, lousy day, how was yours?") that they can either echo or offer a short response to before moving on with the conversation. Exceptions to this are things like a family member being seriously ill or passing away, major life changes (starting a job, starting a relationship with someone, etc.) where, if you're talking with a friend, it should be mentioned so that they have the opportunity to respond.
• Try to be concise / brief when responding to questions or adding to the conversation. For NTs, social conversations are mostly about talking with the other people involved and spending time with them, not about the transfer of information. It can be really tempting to add everything you know about subject X to the conversation, but most of the time the NT participants are only expecting a sentence or two in response.
• Ask people about themselves and what interests them (most people like to talk about themselves, apparently). This will also help you identify what topics people like to talk about.