Crafting Potions & Concoctions
To be able to craft potions, you must build a Laboratory at your Home and have all the ingredients. Click on your laboratory, and in the crafting screen select a recipe or click on ingredients from your backpack. Then click 'Craft'.
When the crafting is complete, you can collect your items. If you left the laboratory crafting screen up, a 'Success!' notification appears. If not, simply click on your laboratory (a purple exclamation point will appear above it when the items are ready) and the crafted items will drop for you to collect.
The Alchemists' Society
The Alchemists' Society is a group of alchemy masters in the world that helps the Ministry of Monsters. They are an elite group of alchemists who require Alchemists' References to be able to join their ranks. Mister Dee appears to be the Society leader.
They have a shop building located in London which sells several different types of alchemy items and potion bundles.