Magicians who create their magical effects by the use of potions and the like rather than through the use of spells are collectively known as Alchemists. Not all alchemists, however, are solely concerned with magical effects; alchemy is a very wide field which covers aspects of all of the physical sciences as well as divination and thaumaturgy.
In game terms, the use of potions is governed by the "Powers with recoverable charges" bit of the rules, or by defining it as an "Expendable Focus". If you want to be able to make the potion yourself, you will need to spend character-points to obtain the power. If a potion is tailor-made for yourself only, it is built straight, but if you want to be able to share it you must take the "Usable by others" advantage. The whole thing can be made "Independent" if the potion is made from a recipe which can be taken away from you, and Independent recipes are the only ones you can steal (or otherwise obtain) and make without spending points. Of course, any potion "Usable by others" can be gurgled down any time and by anyone, whether they have the ability to replace the charge or not.
Potions can be a good way to run your magic if you don't have much END to play with since they don't necessarily have the END requirements of Spells, though they do usually have a reasonably long start-time (finding the flask, opening it and drinking the contents will take several phases, and the onset time before the power begins to operate might be anything from a few minutes to a couple of hours). A potion with an instantaneous effect, such as a Potion of Fire-Breath, should be bought with the "Delayed Effect" advantage unless you want to belch flame the instant the start-time is up.