Symbiosis does 2 things.
1. Makes spells more difficult to cast. This is useful for training because:
1a. It increases the learning cap on a spell. E.g. if a spell normally stops teaching at 800 ranks it might teach up to 1200 ranks with a symbiosis.
1b. It reduces your the max amount of mana you can put into a spell making it more mana efficient to cast spells over and over. E.g. you might normally need to put 80 mana into a spell to learn from it. With a symbiosis you might only be able to put 40 mana into the spell and it would teach the same as the normally cast 80 mana spell. Much more mana efficient.
2. Potentially dds an additional buff to a spell. The default symbiosis, Chaos, doesn't add a buff, but it also doesn't need to be researched ahead of time either.
The additional buffs are specific to which symbiosis you have chosen to research. In your case you have the option to add a Primary Magic (CAST), Attunement (HARNESS) or Arcana (ACTIVATE) buff to any spell you cast. To use your CAST, HARNESS, and ACTIVATE symbiosis just choose which one you want to use and research it. You will be able to use that symbiosis at will without needing to research it again until you choose to forget it to research a different one or die.
To use a symbiosis you just add the step of PREP SYMBIOSIS before you cast the spell:
prep symbiosis
prep <spell>
(optional harness, cambrinth, etc)
cast <spell>
If you have a researched symbiosis, you'll get the normal effects of the cast spell (at the mana level you're able to cast it at with the symbiosis) and the buff from the symbiosis. Because a symbiosis makes the spell more difficult to cast you are effectively trading some potency for the additional buff unless you are able to cap even a symbiotic spell. E.g. if you normally can cast Instinct with at most 80 mana for a +40 Evasion buff, you might be able to cast at most a 40 mana Instinct with the HARNESS symbiosis for a +20 Evasion buff and +20 Attunement buff. Made up numbers.
