As Google typically does upon the release of a new product, it has updated its support documentation with a series of common questions and issues users may find themselves facing when using Wear devices. Some are pretty handy. For example, if your phone is too far from your watch to maintain the pairing connection, you lose voice action controls. You can still set alarms, check your calendar, step count, heart rate, and a few other basic features, though.
There's a list of supported Google Now cards, too. A list of various tips and tricks for interacting with your watch contains a few interesting tidbits. For example, placing your palm over the screen of the watch until it vibrates will dim the screen. You can quickly turn off watch vibrations by swiping all the way from the top down on the screen, and reverse this by doing the same thing again.
Other interesting features like the ability to silence your phone if you're using your watch and the hotword for going to your watch's settings menu are in there, too. A primer on Wear notifications can be found here. A rundown on basic tasks that be accomplished with Wear gives you probably the best overview of what you can expect your Wear device to do, apart from whatever functionality 3rd party apps will eventually provide. You should also know that only a handful of Google apps actually work with Wear right now, including Google Now, Hangouts, Gmail, Keep, Maps, and Calendar. Chrome, Drive, Google+, the Play Store, Google Photos, Wallet, and YouTube do not currently have any Wear integration. If you're worried about Play Music, don't be - it functions through the Wear media controls like any other music app.
Finally, there are even a few apps specific to each OEM's watch, too. The G Watch will include a compass app and a world clock. The Gear Live will have a heart rate app, a compass, and a stopwatch. Interestingly, Wear has its own native stopwatch, too, though apparently Samsung and LG are opting for their own versions.
You can learn more about Wear at the main support portal for it, here.