At least two meanings.
A preposition describing a location.
in my heart
Nasa Pilipinas ang pamilya ko.
My family’s in the Philippines.
The question word for asking the location of something is Nasaan.
Where’s the car?
Nasa bakanteng lote.
It’s in a vacant lot.
Unrelated to the above… As a noun, the word nasà means a wish or desire. It is frequently seen in conjugated form.
to desire something