Lemmy is not one big application like reddit. Instead everyone can download Lemmy and host their own >instance<. Each instance can have their own users, their own communities/subs and admins.

Since Lemmy is part of the >fediverse<, it means that each Lemmy instance can interact with each other, and can even interact with other applications of the fediverse (like mastodon, which is more similar to twitter).

Because everyone can make their own Lemmy instance, it is also possible for bad faith actors to make one. They could create many accounts on their own instance, and try to mess with the other Lemmy instances by either posting a lot of comments, reporting a lot of content, or a number of other things. To prevent that from being an actual issue, each instance has the option to >defederate< other instances. (I am not 100% sure on the following so please correct me if I'm wrong) Defederating means that users of instance A cannot interact with the content or users of instance B, if instance A defederated instance B.

Since the performance of website is dependent on the instance you use, you can try to find another instance with less users and a more stable server. As long as it is not defederated by many other servers it will be effectively be the same experience as being on another instance.