Though Android Wear Smartwatches are capable of running regular Android apps, the installation of apps is not straightforward. It requires setup Android SDK on your PC, a working ADB (Android Debug Bridge) connection to your watch and need to enter commands manually. However, Android Wear APK Tools makes it super easy to install Android apps on your Smartwatch.
Android Wear APK Tools is a GUI application for Windows, Mac and Linux and lets you easily install and uninstall apps (non-protected APK) on your Android Wear smartwatch. You do not need to enter commands manually into the Command Prompt or Terminal.
All you need to connect your watch to your computer, select the APK and hit the install button. Make sure to enable ADB Debugging on your phone and your watch. Also, make sure to have Android SDK and required drivers on your computer.
Android Wear APK Tools is a free app and supports Windows, Mac and Linux. The installation process takes just a minute. Download and step-by-step installation instruction is available at this XDA thread.