Do you have to have an iphone for it to work?

Yes. Some functions will only works if you have an iPhone 5 or later

Set up your Apple Watch - Apple Support

Set up and use Apple Pay with Apple Watch - Apple Support

The watch won't function at all unless it's paited to an iPhone 5 or later

The Apple Watch must be within Bluetooth range of the iPhone with which it is paired, to use most of its functions.

From the manual, p.19:

If your Apple Watch and iPhone are on the same network but aren’t connected by Bluetooth, you can also do the following on Apple Watch without iPhone:

• Send and receive messages using iMessage

• Send and receive Digital Touch messages

• Use Siri