This expression is mainly used in Britain. It is often used immediately after a set of simple instructions and roughly means the same as '... and it's as simple as that!'
In 1887, British Prime Minister Robert Gascoyne-Cecil appointed his nephew Arthur James Balfour as Minister for Ireland. The phrase 'Bob's your uncle' was coined when Arthur referred to the Prime Minister as 'Uncle Bob'. Apparently, it's very simple to become a minister when Bob's your uncle!
‘How do I get to your house?’
‘Take the first turn on the right, walk about 50 meters and Bob’s your uncle.’
