“um” is an expression of confusion or a space filler in conversation like “uh”.

“Um, how do I use this tool again?”

just a guess, but "unofficial manpage"

Since they are "your own manpages", I would've guessed they are "user manpages"?

This isn't a bad guess! I don't know why it was downvoted.

It's a thing you say when you don't know what you are doing or can't remember a thing.

one in portuguese