Since this word is made up of a single kanji, it should use the kun'yomi reading. When learning the kanji, you didn't learn that reading, so here's a mnemonic to help you with this word:
You go off to the west. It's the Wild West, even. There aren't many people out here, making it easy to find a niche (にし) for your snake oil business.
The building on the west side of the hospital is my apartment.
Darin is heading west.
Meanwhile in West Portland, the Crabigator was crossing the road.