This article explains how to use Photoshop's Photomerge feature to create panoramas, before-and-after comparisons, or photo collages in Photoshop. Instructions apply to Photoshop CC 2019 for Windows and Mac.
Whatever you want to create with the Photomerge function, the process is always the same:
Open Photoshop and select File > Automate > Photomerge.
Select a layout on the left side of the Photomerge dialog. The choices are: