Continuing the discussion from Mona, Mastodon apps and a screenshot Easter Egg :
Instances are Mastodon servers that people have set up. Some are their own personal instances, some allow others to join. Servers store posts, send them to other servers, and receive posts from other servers. It’s not like Twitter, Facebook, et al. where there is one central place for everything.
Since instances are run by people, groups, or companies, they can cater to people with common interests, or just general interests. For example, one of the instances I have an account on is fediscience.org, which caters to scientists. I’m also on fosstodon.org, which caters to people interested in free and open source software, SDF that supplies computing services and caters to artists. A couple of others are mastodon.social, and masto.ai. Since servers cost money to run, some servers limit the number of users. For example, mastodon.social has about 150k accounts, and no longer accepts new accounts.
Whomever is running the instance sets the rules. You can go to their website, create an account, and see their rules. Some sites allow literally anything. Some allow only on-topic posts for whatever their interest is, and there are thousands in between.
Now. Instances are federated, meaning they can send and receive posts from other instances. So in your feed, you’ll see
Local which are things people have posted on the instance where you have an account. You’ll also see
Federated, which are posts that come from other instances.
Recall that some instances allow anything, therefore, the instance you are on might choose to ban instances that do things they don’t agree with. For example, if you have an account on the
First On Race Day instance for people that love Ford vehicles, they might choose to ban the instance
Fix Or Repair Daily. That means you won’t see any posts from that instance.
Mastodon is part of the Fediverse, a group of servers that exchange information (hence, the names like
fediscience). The Fediverse also encompasses services like Friendica that allows sharing open source software, and PeerTube for sharing videos.
As I said, I have accounts on multiple instances. If you develop a following on an instance, and then want to move everything to another instance, from what I understand, that is possible, so you needn’t fear that you’re making the wrong choice.
Also, the culture on Mastodon is different from other social platforms, and is generally more inclusive. One example is that when people post images, it is expected that they will add Alt text to describe what is in the image for people who have low vision or are Blind.
There are several websites that say they will help you find an instance that caters to your interests or criteria. Probably a Google search is the best place to start.