Since this was 8 hours ago I guess you've probably figured it out already. But just in case.

There are a few ways you can find new communities, but as far as I know there's no easy way on Jerboa which is probably why you're confused. Luckily the mobile site works great, especially on Android as you can install it as an app to your homescreen.

So get logged in in a browser, mobile or desktop. Now:

1. You're on lemmy.world, so you could visit "communities" at the top of the page when logged in and filter by "local" (for communities hosted on lemmy.world) or "all" (for all of the communities lemmy.world knows about, regardless of where they're hosted) and do a keyword search or just see what catches your eye. Clicking through from there will take you to a local version of that community where you can subscribe from the sidebar.

2. Alternatively you can use an external site like lemmyverse.net, which lets you set your home instance via the home icon in the top right. Then when you find an interesting looking community, you can click straight through and again it'll be a local version of that community so you can subscribe to it from the sidebar.

If you find yourself "logged out" when viewing a community, it just means it's on another instance and you've gone to the original URL instead of your local lemmy.world one. Do not panic. Just follow the instructions in the sidebar to get back to where you want to be.

This all sounds very complicated but once you've done it a couple of times it's just second nature.