Ñapa is a colloquial term, particularly common in Latin America, for a little extra something given for free, often as a bonus or a small gift thrown in with a purchase, like a baker giving you one extra cookie.
In this song, the line "Si me gusta yo te doy la ñapa" ("If I like it I'll give you the bonus") uses the word playfully and suggestively, implying that if she's interested in someone, she'll give them more than they bargained for. It's a fun, flirty way to tease without being too direct.
"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.