Craft a Brewing Stand
Get Blaze Powder to fuel the Brewing Stand
Get Glass Bottles
Fill the Glass Bottles with Water
Get a Fermented Spider Eye
Place the Water Bottles in the Brewing Stand
Add Blaze Powder as fuel
Add the Fermented Spider Eye to brew a Potion of Weakness
Use Gunpowder if you want a Splash Potion of Weakness
Use Dragon’s Breath if you want a Lingering Potion of Weakness