Android Wear has a finicky way of launching apps on your wrist. As I previously covered, you can use voice commands or navigate to the launch menu using a series of taps and gestures. And if I'm being completely honest, the current launch method flat out sucks.
Thankfully, developers exist and often provide a means for fixing issues such as this one.
To access the launcher you only need to swipe in from the top-left corner for the screen. As your finger moves across the screen, a list of your installed apps will display in a scrollable list. From here, launching an app is identical to the process you would find on any current smartphone -- just tap on the icon.
If for some reason you're having a hard time getting the launcher to actually launch, you'll need to resync your installed apps. You can do this by launching the Wear companion app on your Android device, tapping on the settings icon, and scrolling to the bottom. If problems still persist, try restarting your watch.
In the little bit of time I've been using the launcher on my watch, I've had no issues. A short vibration occurs as I open the launcher, which is a nice indicator that I'm not going to accidentally clear a notification card.