To make a Potion in Minecraft, you need these things:
A Brewing Stand for brewing potions.
Blaze Powder for fuelling your Brewing Stand.
Glass Bottles to contain your Potions.
A Water source nearby (Cauldron or Water block).
Every potion starts with a Water Bottle. To make a Water Bottle, just right-click on a water source with a Glass Bottle in your hand.
There are three steps to making a Potion:
Make an Awkward Potion (Water Bottle + Netherwart) in the Brewing Stand.
Add an effect ingredient to specify the Potion effect.
(Optional) Add one or more modifier ingredients to change the nature of the Potion.