Per rule #3, we don't offer support in this community - please check the sidebar for a list of communities that can help you out with this question.

If you go to https://lemmy.ml/communities then click All you will see communities from all federated instances. Communities from other instances will have @<instance> displayed. If you don't see one in specific you can search for !<community>@<instance> (you may have to wait a minute and search a second time if it's the first time anyone has searched for that community).

As far as browsing those other communities, that will be https://lemmy.ml/c/@. For example https://lemmy.ml/c/guitars@lemmy.world

In Lemmy, subreddits are known as communities. You join a community by its name, for example !mycommunity@example. Do a search for that community, click on the search result, and you'll be given an option to subscribe. Note that the search might come up as 0 results even though you got the community name right. It's just taking longer to find the community.

to subscribe to communities in other instances, search for them, go to community, look in the sidebar and hit subscribe. For example to subscribe to !nostupidquestions@lemmy.world click that link, look in the sidebar, hit the subscribe button.

You need to join through your home instance (lemmy.ml) like going to https://lemmy.ml/c/foodporn@lemmy.world if someone from your instance has subscribed to the community or go to lemmy.ml and search for !foodporn@lemmy.world (you might have to wait a bit)

I would like to know that, too.