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Somewhere on the flash there will be a sliding switch or rotatable dial that allows you to set the flash to either manual, auto range bright green, auto range blue-green, or something designated by the light blue sun.

The chart on the back shows a table with a range of film speeds and corresponding distance and aperture pairs.

The cells which are coloured bright green show the aperture to set for that auto range and the corresponding film speed. As an example, ISO 100 film requires f/4 if you are using that auto range. The numbers in the left two columns indicate the maximum distance to use for that range - 18 feet in the case of the bright green auto range.

The blue-green auto range permits use from farther away (up to 36 feet) but you have to use an aperture which is two stops larger (f/2 for ISO 100).

If you don't wish to use the auto functions, you can use the individual cels in the table to determine which aperture to use for which film and distance combination.