Apple Watch
Does the Apple Watch series 5 work with the carrier Metro PCS? Ask a friend
The GPS only Apple Watch can do Everything the cellular model can do as long as your iPhone is nearby, where nearby is somewhere in the same 3-4 bedroom home (assuming typical wood frame construction).
https://support.apple.com/en-us/HT205547
The Cellular Apple Watch allows you to leave your iPhone at home while you go for a walk, run, bike ride, etc...
The Cellular Apple Watch shares the iPhone's phone number. This requires the iPhone cellular carrier to support the Apple Watch. The iPhone carrier charges a monthly fee for this service. In the U.S. the fee is $10 per month added to your iPhone bill.
iPhone Cellular Carriers that support the Apple Watch, which models, the radio frequencies each model uses, and the country where they offer service:
