I wanted to create a new event (which goes into your calendar) and not a reminder, which doesn't show on the watch. I looked in the manual and the following does not work - there is no + icon to click to add a new event. Tapping the day of the event launches a long agenda list of events which you can scroll through, which is certainly helpful. But there is no ability to add an event anywhere.
Create an event
You can use your Calendar to create events.
1. From Apps, rotate the bezel and tap
2. Tap the day of the event, and tap Create
event. Enter the event details, and set a
3. Tap Save when finished.
At step 2, on my Gear S3 using One UI v1.0, there is the + icon at the top of the screen and a create event button under the "3 dot" menu. Either option starts the Create dialog.