Apricorns can be found on Apricorn trees, and are used to make Poké Ball discs. In order to make discs, the apricorns must be cooked into cooked Apricorns in a furnace. All discs are made with color patterns in a row in a crafting table. Crafting the different kinds of Poké Ball discs requires combining different colored cooked Apricorns in a pattern (e.g., 1 cooked Red Apricorn in the middle of 2 cooked Blue Apricorns will produce Great Ball Discs). The discs can then be used with an anvil and a hammer to make the corresponding Poké Ball Lids.
The recipes for crafting different Poké Ball discs is on the Poké Ball Discs page.