Apricorns can be found on Apricorn trees or by using Forage on leaves with a Bug-type or Grass-type Pokémon. They used to make Poké Ball discs, needed to make Poké Balls. In order to make discs, the Apricorns must first 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., one cooked Red Apricorn in the middle of two 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 are on the Poké Ball discs page.