Typically your printer margins will be provided on your checklist.
Each printer has different printer margins.
To check what your printer margins should be for the printer you are assigned go to printer setup, click test print and a margin ruler will print out.
The test print page will show you a ruler guide. On each side follow the diagonal line, where the line runs off the page is what the margin is for that side.
In this example the top line is 15, right line is 25, bottom is 18, left is 20.
When your margins are set wrong, it will be most noticeable on your digital jpeg files. You will see a white line with layouts with coloured backgrounds. Also if your photos are not centered on the layout, you can adjust your printer margins to shift your images or eliminate the white line.