You’ll need an iPhone with that
Late last year when Apple launched WatchKit, the set of tools which allows developers to make apps for Watch, a number of limitations became apparent. The most obvious is that, for now at least, you’ll need an iPhone in order to use many of the features of Apple Watch. That’s because all the code used to build apps is stored and executed on the iPhone and the results passed to Watch to be displayed. When you interact with Watch, the details of the interaction are passed back to the iPhone, the relevant code executed, and the results again sent to Watch. It also means that to download apps to Watch, you’ll have to download them first to your iPhone and then ‘send’ them to Watch.
Although Apple hadn’t confirmed it at the time of writing, a beta version of iOS 8.2 contains a companion app which allows Watch’s settings to be customised. That suggests that when Watch ships, you’ll configure it from an app on your iPhone.
At WatchKit’s launch, Apple said that, starting some time in 2015, “developers will be able to create fully native apps for Apple Watch”, which suggests that eventually you won’t need an iPhone to use most of Apple Watch's features.
The Watch’s reliance on the iPhone isn’t all bad news. It works as a remote control for the iPhone’s Music app, for example, and in place of your iPhone to authenticate purchases made with Apple Pay.