"Complications" sounds a little complicated but actually they are a great vehicle for making your favorite app so much more accessible on your Apple Watch.
When you raise your arm you see your watch face - like this.
Assuming that you want to start your newest App on your Apple Watch - in this case the voice recording App Mike you´d have to tap the digital crown for getting to the homescreen.
Then you´d have to tap the App Icon Mike and could start the recording. Mike is a Voice recording App. So if you have an idea when on the go and you want to voice record it then you don´t want to start the app from the homescreen.
That´s one inconvenient step more instead of starting the app directly from the watch face as a complication.
By enabling your favorite App in your watchface you simplify the usage of the app - and you will use it much more often.
So is it complicated to add an App as a complication? No, actually it´s easy. So look here:
Select the watchface of your choicePress firmly on the watchface until the watch responds with a tapTap "Customize"Swipe left until the configurable complications are shown and select the complication you´d like to change by taping on it.Turn the digital crown until the respective app complication is shown. Push the digital crown one more time - Done!
From now on you can easily start your favorite app from the watch face by just tapping the complication.