"A bit" is similar to "a little", "kind of" or "somewhat". It's used when you want to lessen the degree of a description:
He's a bit shorter than me.
He has a video of me from when we were in college that's a bit embarrassing.
"A bit" is used for adjectives that are negative. So you wouldn't say that an event was "a bit fun" or that a person is "a bit nice". But you can say that the event was "a bit boring" and the person is "a bit rude".
kind of > a little > a bit > somewhat