Messaging from an Android Wear watch is not always the easiest task, although it has become easier now that Hangouts has full support on Android Wear meaning you can actually send messages and initiate them instead of just replying. Not everyone has the opportunity to type up messages though, and in such cases it would be much easier to use something like video messaging or speak to text to communicate. The only issue here is that most Android Wear devices don't have built-in speakers, save for the Huawei Watch and the ASUS ZenWatch 2, and even those don't work just yet as the software doesn't support them, so playing any video messages would require the use of headphones.
The good news is that the Android Wear 6.0 marshmallow update opens up support for those speakers essentially making them useful and both the Huawei Watch and the ZenWatch 2 will be able to take advantage of that. Also taking advantage is an app called Glide Video Chat Messenger which has added support for Android Wear so the app can be used on those two watches with speakers, making it much simpler to communicate and watch video messages from anyone who has sent one your way. It's also worth noting that Glide's addition of Android Wear support extends to all Android Wear smartwatches and not just the two mentioned here, but any audio that's needed to be listened to would have to be played through Bluetooth headphones to hear it.
With Glide installed on Android Wear users will be able to view and listen to incoming video messages and to reply they can either record a message of their own from the watch (without the video capability since the watches don't have cameras) or they can type messages to respond. While Android Wear 6.0 has not necessarily reached all Android Wear users just yet, as that will take some time, the update to Glide Video Messenger should be rolling out to just about everyone through the Play Store today. If you're new to Glide you can pick it up from the Play Store link, and if you're an existing user then you should see an available update in the my apps section if the update has reached your device.