How do I find out the additional 3 effects of ingredients?

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.

This webapp will help you figure out available combinations based on the ingredients you have. this is an APP i use to figure out what ingrediants do what and what potion is worth more since leveling in alchemy is determined by this. i'm a new user just trying to share a resource since i haven't seen one like it listed on here...

I use this link and have learned all four uses of an ingredient. You can also level up your alchemy and put your perks to learn the first 3 uses of an ingredient. If you want potions with more than one effect example: Damage health damage magic. Go to the potion ingredients you want to mix. Choose 2 ingredients for your first vial and then look at the second potion you want to have the extra effect. Make sure that one of the ingredients listed for the first part of the potion is in the second additive for a potion.

http://m.ign.com/wikis/the-elder-scrolls-5-skyrim/Potions