Click on the tab Magazines at the top, select local and federate, put lemmy.world in the search box to see all lemmy.world communities. If you want to check for community with certain keywords you can try putting [keyword]@lemmy.world. It can search for the keyword in both the name and description, but not extensive as if you'd search on lemmy.world.
This can use some improvement, but it's not a Kbin problem though, since Lemmy is even worse when it comes to searching for communities outside each instance.