Completing the story quests in Revenant Act 1 will lead you through the tonic crafting process, which is generally pretty easy to understand. What's more confusing is what to do to get more tonic recipes and expand your repertoire.
Unlocking tonics is easy--you just need to craft more tonics. You start with a series of tonics whose icons have green borders, indicating that they're the Uncommon level of rarity you see on weapons and armor.
If you craft the green version of a tonic several times (it seems to be about five), you'll unlock its blue version, the Rare rarity. Keep crafting a blue tonic to get the purple, or Legendary, version.
The trick here is keeping yourself filled up with reagents, the materials you need for crafting tonics. You can earn these from killing enemies and completing activities throughout the solar.
[
Collection
]
[
|
...
]