First up, you can pick the featured color for the face. Many are designed to compliment the same color Sport band. Since my watch is a space black stainless steel model, I’m selecting the multicolor option.
With five available complications on that specific face, you can then scroll down and select one for each slot. When you do so, a preview will appear on the watch face at the top of the page to give a better idea of what to expect.
When done, hit Add, and the face will then be sent to your watch. In my case, it appeared instantly. It is also added to the My Faces section in the My Watch tab on the app. You can view every face and reorder them or delete one by selecting Edit.
As always you can also change faces directly on the watch. A simple swipe gesture on the screen will flip to the next face. Force Touch a face to bring up the customization options.