Easiest thing to do, click Communities up at the top, then click "All" right below "List of communities"

This will show you all of the communities from all of the federated lemmys (sorted by number of users), and allow you to subscribe to them and easily interact with them from your lemmy.world account. Once you subscribe to the ones you want, you can go back to the main lemmy.world home screen and click Subscribed, which will give you a list of posts from your subscribed communities, much like the Reddit home screen.