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a. Open a new file, make its dimensions are 16 x 16 px.
b. So we can see what we are doing fill your background layer with white. Hit D to reset your colors then Alt + Backspace to Fill.
c. Go to Edit>Preferences>Grid, Guides and Slices...
and use these settings:
Gridline every: 16 pixels
Subdivisions: 16
d. Hit Ctrl + ' to toggle the grid
e. Now go to Window>Status bar. It should be at the very bottom, make sure it's checked.
f. Now in the bottom right corner there is a number, it should say 100%, click on the number and change it to 1600%. This is the amount the image you are working on is zoomed in on. After you zoom in your image will look like this.