If iNat doesn’t already have the boundaries for your town, you’ll need to create a place for it, which will require that you have 50 verifiable observations (has a date, a location, image or sound, and has not been voted captive/cultivated). Then go to https://www.inaturalist.org/places/new to set up your place.
You can read more about projects here: https://www.inaturalist.org/pages/managing-projects
It may be worth noting that currently projects don’t allow Lists as taxon sources, you’d have to enter each one. (Though that may change in the future.)