Every ingredient for things you can make in Skyrim has 4 effects. The first one can be discovered by simply eating the ingredient.
I know that the first and second one together can also be found out if you have the right perk for it in the alchemy tree.
But how do I get to the other effects?
Best Answer
Trial and error by brewing potions. If you match 2 ingredients that have an effect in common, you produce a potion/poison of that effect. There is also the Experimenter perk in the alchemy tree which lets you see more effects by just eating the ingredients.