I try to explain this in a structured way, so that you hopefully don't feel too overwhelmed. Feel free to ask if something doesn't make sense.

Lemmy

Lemmy is like e-Mail, there are multiple websites where you can make an account, but you can still communicate/participate with users from other sites. (This is called decentralisation.)

Instance

An instance is a website that you use for logging in to Lemmy. You only need an account on one website to participate (e.g. writing posts/comments) in Lemmy.

So, since you already have an account, that means you already have chosen an instance, it's lemmy.world.

Community

Like users, communities can be created on different instances. There can even be a community with the same name on two different instances.

For example:

• lemmy.world/c/Autism
• lemmy.dbzer0.com/c/Autism

These communities can still be accessed on your instance, they are all synced. (With some exceptions which I'm not going into right now.)

How to participate in communities of your instance

1. Go to your instance (lemmy.world)
2. Log in
3. Go to the community you want to participate in (lemmy.world/c/Autism)
4. You don't need to "join" a community, but you can subscribe, so that new posts show up in your feed

How to participate in other instances

1. Go to your instance (lemmy.world)
2. Log in
3. Go to the community you want to participate in but add the instance to the back like this: lemmy.world/c/autism@lemmy.dbzer0.com
4. You don't need to "join" a community, but you can subscribe, so that new posts show up in your feed

So in summary it's the same Aso for communities of your instance, just make sure to always start/login on your instance.

Direct links

Since constructing the URL like described above is quite annoying, Lemmy can use special links that work across all instances. They are as follows:

• !autism@lemmy.world
• !Autism@lemmy.dbzer0.com

Apps

There exist many Lemmy apps. They can facilitate things (especially when you want to browse on your phone), but this also means that the look&feel is different. Some step by step guides might not work exactly the same on different apps.