Oleo saccharum is citrus sugar extracted from citrus peels. You can then take those sugar-coated peels and put them in a food dehydrator to make dried candied peels as a garnish or snack. 

Simply: 

• Peel citrus
• Cover peels with sugar and let sit overnight. The sugar will pull out citrus oils and turn into syrup
• The next day or two, use your fingers and wipe off the syrup from the peels and place in a dehydrator (or in your oven on the lowest setting)
• Reserve the flavored sugar syrup to use in cocktails. I use mine in Old Fashioneds (orange oleo) or in Ti Punch (lime oleo).
• After the peels are dried in the dehydrator, store in an airtight container and enjoy.