Just had a question about this, thought it might be useful to answer as a post:
There are lots of different server types on the Fediverse, but they talk to each other using a common standard called ActivityPub.
This means you don't need to be on the same server type to interact.
For example, if you're on a Mastodon server you can have a conversation with someone on a Friendica server.
This works even when the server types are very different. People on Mastodon etc can like, comment and share videos from @peertube or follow livestreaming accounts on @owncast. (To see examples, take a look at @FediVideos)
This process is so seamless that you may not even be aware you're interacting with people from other server types. If you're a Mastodon user, try clicking on @bobfisherphoto and it will look like a Masto account, but it's actually a @pixelfed account. To see what an account "really" looks like, click on the avatar on its profile page.