Use the editor to create a base template of your design - All text and images that you add to the template are objects that can be modified via the API.
Step 1: Create a template with the editor
To create your own template start with a blank or pre-created template. In the editor you are the designer - and you can add images / GIFs / texts.
The editor consists of layers - each layer can be changed with the API. Text and images will automatically resize to fit the box in the editor.
Step 2: Name the layers
Make sure each layer name is unique.