Refugee Redditors as they make the move.

So each lemmy site is an instance with its own servers. Even though they all connect to one another, they run on their on load and data. So you're on lemmy.world, which is being very overloaded with the influx of reddit folks. I'm on lem.ee which is buttery smooth, yet still able to see posts and comments from world, since it's all federated

You just make an account on a smaller instance (easiest way to find them is at the bottom of the page here), and subscribe to all the communities you want from lemmy.world and others to start pulling them in.

Then proceed to shitpost as normal.

EDIT: Alternatively, go here, switch the "Software" option to Lemmy at the top, and look for a server geographically close to you.

Go to literally any other instance and create an account there

For a bit more context on what others have already said, Lemmy is more decentralized, akin to email. Lemmy.world is the biggest website for Lemmy, in the same way Gmail is for email, but like email, there are tons of smaller or even personal sites that can all network together. If one site goes down, only content on that site and its users are affected, others are not.