Templates are "models" that you can use as a starting point for new designs. Instead of starting from a blank canvas, you get a new design that includes the layers from the template plus your uploaded photo.
For example, Image 1 is a template. It contains a background with an athlete, some text, a white box, and a running shoe. The running shoe is set to be a replaceable subject, which means it will be swapped out for a photo automatically.
Images 2 and 3 are designs that are made from the template. For those, we uploaded a photo of a running shoe and applied the template. This gave us a design that matched the template, but with our photo replacing the shoe layer. To create the unique designs, all we had to do was edit the text and change the color of the background and athlete. So much quicker than adding all of the design layers from scratch!
To get started with templates, see:
Templates in Batch Mode:
Apply a custom template to multiple images in Batch Mode