Witchcraft is usually an ability that is passed down through the generations. Your character may have learned from a mother, grandmother, great-grandmother. However, it is also possible to have been taught by a witch who took you under their wing for some reason. A best friend witch, a witch who took you in as a child when you showed up on their doorstep, etc.
Every organic material is magical energy within it. Some, however, have much more magical energy than others.
Witchcraft is the art of mixing these organic materials to create new substances that can accomplish various goals. Sometimes simply mixing the ingredients together is enough, while sometimes heating the ingredients in specific ways, crushing ingredients, cutting them, etc. are needed in order to release the magical energy and create spells. Witches also have the ability to read tea leaves in order to look into a person's future. There are several humans in cities who claim to have the ability to see into the future, but most of them are not true witches. The tea leaves can only be interpreted correctly by very skilled witches.