In a few days monsters (when killed) will drop ingredients that can be used for Alchemy, some ingredients will be more rare than other.
Alchemy is a sub-type of wizardry . Being an alchemist is easy; you need to satisfy the following:
* Be able to cast the alchemy spell.
* Have access to a cauldron ( can be bought in shop )
* Have some ingredients.
To create something put ingredients in the cauldron, then cast the 'alchemy' incantation . You might make something

. Be warned though! backfire effects are possible, especially if you throw a lot of stuff in the pot. In fact, the more junk which is in the cauldron, the worse any potential backfire is likely to be. Backfire generally occurs when you get the ingredients wrong but low-level alchemists attempting very difficult (4+ ingredient) formulae may have problems too!
In order to get better at making stuff, you will need to learn the alchemy skill. Books found in shops (and elsewhere) will give you formulae for making stuff