You'd search their address in the search function, so if you wanted to follow the fedia worldnews magazine, you'd search "<at>worldnews<at>fedia.io" replacing <at> with @ and it'd pop up. BUT, kbin.social is currently not federating with other instances, so this doesn't really work right now, though it will soon once things are more stable. I suggest playing around with this on another instance or app like mastodon!