The profession Alchemist can be obtained by taking a orange box "Alchemy Kit". You can get this profession at the start of every Survival game.
The starting skill of the Alchemist is called "Create healing potion" Which uses a plant called shimmerweed.
This skill is the most basic of the all.
After obtaining a few profession levels, different Plants and Power Crystal would be needed to make other potions.
You can hold in your inventory all the same plants and create its minor potion first. Then making the advanced one to save mana.
If the Constructor slips his mind and forgets to build you a herb bed, it is best to change to another profession.