If you want to have your own in home WIFI then yes you'll need an internet provider and internet service along with a modem and WIFI router.
Most modems that you get through your internet service provider now include WIFI built in.
You can get WIFI without your own internet service through free WIFI access points such as Mcdonalds, Lowes, Home Depot or even a public Library.
Other than that you'll need internet service at your home to get in home WIFI.