What does "Bob's your uncle" mean — and why is it funny?

informal, British

Meaning

And there you have it; the task is done and it was easy. Said at the end of a simple set of instructions.

Where it comes from

Often linked to 1887, when British Prime Minister Robert ('Bob') Cecil appointed his nephew to a senior post, making 'having Bob as your uncle' a shorthand for an effortless advantage.

Why it is funny

It is funny because it name-drops a relative who does not exist for the listener. The phrase pretends to explain something while telling you nothing, and the cheerful nonsense of invoking a random uncle as the final step lands as a small absurd flourish.

Used in a sentence

"Twist it left, push down, and Bob's your uncle — the door's open."