Brand New Key" is a pop song written by folk singer Melanie, which became a novelty hit in 1971-72. Taken from Melanie's album Gather Me, it was also known as "The Rollerskate Song" due to its chorus. It was her biggest hit, reaching #1 on the Billboard Hot 100 singles chart in December 1971 and January 1972. It reached #1 in Canada and Australia, and #4 in the UK charts.
The song is lighthearted in tone, sung from the viewpoint of a girl with roller skates trying to attract the attention of a boy:
I got a brand new pair of roller skates,
You got a brand new key.
I think that we should get together and try them out, to see ...
The roller skates in question would have been children's quad skates, which were clamped to the soles of ordinary shoes. The clamps were tightened with a special "key" that basically was a very simple socket wrench. The key was inevitably lost or misplaced, in which case a screwdriver or other tool usually could substitute though at some inconvenience. Although the lyrics claim that the roller skates are "brand new"; the girl presumably has lost her key:
I roller skated to your door at daylight[...]
I'm okay alone, but you got something I need