A few example of back-rank mates delivered by a queen:
Once again, beginners shall not forget the king has the most value of any piece, and sacrificing the queen to deliver the mate is worth it.
An example showing a queen sacrifice
A promotion can also lead to a backrank mate:
A back-rank mate by promotion
Promotion followed by checkmate
Back-rank mates are checkmates to the opposing king delivered by a rook or a queen on the rank where the opposing king started. The opposing king is trapped by his own pieces, unable to escape the check.
On the lower levels of ELO, this checkmate pattern is often encountered, and fairly common. Sometimes, sacrificing lower-value pieces is required to delivered the checkmate, but it is worth it since it is, well, checkmate.