Gather ingredients: water bottle, fermented spider eye, nether wart
Brew a Potion of Weakness in a brewing stand
Place the brewing stand on the ground
Add water bottles to the brewing stand slots
Add nether wart to start brewing
Wait for the awkward potion stage to complete
Add fermented spider eye to transform the awkward potion into a Potion of Weakness
Collect the Potion of Weakness from the output slot