Hi there! Looks like you linked to a Lemmy community using an URL instead of its name, which doesn't work well for people on different instances. Try fixing it like this: !linuxhumor@lemmy.ml
It's also helpful to note that “shell builtins” don't typically have man pages (at least for BASH). You can find help on these commands by typing [builtin name] --help or looking in the shell's man page or info doc (no one told me when I was learning, so I got confused as to why some of the more common commands didn't have man pages)