STV with a single winner is like holding multiple elections where the biggest loser gets eliminated each round. You can vote for your favourite uncle first, because you’d really like him to win, but because you’ve put other people at 2, 3 and 4 you still get a say who wins even though your uncle only got 7 votes. Your Single Vote gets Transferred to your next preference when he’s eliminated.
STV with multiple winners is the same but you stop eliminating people when you’re down to however many you need.
That’s a separate question.
STV with a single winner is like holding multiple elections where the biggest loser gets eliminated each round. You can vote for your favourite uncle first, because you’d really like him to win, but because you’ve put other people at 2, 3 and 4 you still get a say who wins even though your uncle only got 7 votes. Your Single Vote gets Transferred to your next preference when he’s eliminated.
STV with multiple winners is the same but you stop eliminating people when you’re down to however many you need.