Ñapa is a colloquial term, particularly common in Latin America, that refers to a little extra something given for free, often as a bonus or a small gift with a purchase. Think of it like a baker giving you an extra cookie.
In this song, the artist uses ñapa in a suggestive way, implying that if she likes someone, she'll give them more than they asked for, an enticing
"CHAPA" is a fast, hook-driven dembow track from Dominican artist Yailin la Más Viral, featuring Puyalo Pantera. The whole song is built around one chanted call-and-response line ("quiere chapa, toma chapa") that repeats until it becomes almost hypnotic, the kind of hook made for shouting along to in a club rather than sitting down and reading.
Once the verses come in, Yailin raps with total confidence about sex and desire, daring her partner to keep up with her. It's explicit and unapologetic, in the tradition of a lot of current dembow, and it's more about attitude and rhythm than storytelling.