I bought only 2 recipes from some merchants. Now I have to use trial an error to discover the rest of them. Do you guys just write them down on a piece of paper? Or maybe there is some kind of an in-game notebook where I could put it in? Should the player know all the recipes by heart?
Every time you create a potion or poison you will learn that the ingredients used have the given effects. Then when you want to create say, a potion of invisibility, you open the alchemy interface and select (on the left side) ingredients with invisibility.
This will show you all the ingredients you have on you that you know have an invisibility effect. Then you just create a potion out of them.
So no, there is no way to write down "Nirnroot + Death Bell = Poison", but you can go "I want to create a poison, what ingredients can I use". Of course, if you really want to write it down, there's always pen and paper.