To get a fermented spider eye in Minecraft, you need to craft it using three ingredients:

• 1 Spider Eye (dropped by spiders)
• 1 Brown Mushroom (found in dark, damp places, mushroom fields, or obtained from mooshrooms)
• 1 Sugar (crafted from sugar cane)

Steps to craft:

1. Open the crafting table menu to access the 3x3 crafting grid.
2. Place 1 spider eye, 1 brown mushroom, and 1 sugar anywhere in the crafting grid.
3. Collect the fermented spider eye from the result slot into your inventory.

This item is used primarily in potion brewing to create potions like Potion of Invisibility, Potion of Slowness, Potion of Weakness, and Potion of Harming by corrupting other potions. In Creative mode or certain game editions, you can also get it by the command: /give @p fermented_spider_eye 1 This crafting process is simple and essential for potion making in Minecraft.