Kelvin Smith Library
While your collage file can be of any dimensions, it is important to establish a canvas size at the start and set the resolution to 300DPI.
This Photoshop Template can be used to start your collage. It is 24"x18" @ 300DPI.
If you would prefer to start from scratch:
In Photoshop click File > New
That's it! Once you get started, be sure NOT to Crop or Rotate the entire canvas.
Your layered file will save as a Photoshop Document. The final file should be exported as a JPG file (see next tutorial).