The game comes with a manual in PDF format. Check your Start Menu.
However, some elements can only be discovered in game.
Mixing Potions:
Near the end of level 2, you find a bag that contains the Mortar and Pestle, as well as a scroll that describes the ingredients for two simple potions. Simply rightclick the M&P like it was a bag, and place the ingredients in to brew the potion. You can also experiment and try to make other potions.
Casting Spells:
Rightclick a blue hand or a staff icon to cast a spell. The character's quickview is replaced by the rune system, where you can cast spells by entering the correct rune combination. You will come across scrolls that will tell you the correct rule combination for various spells, but you can also try some yourself.
However, each spell has a minimum skill level, so you can't find spells without advancing the correct skills far enough.