Art by Alyssa Williams, again.
Familiars are animals that aid witches in their craft, many witches have cat, toad, or bird familiars, but any animal can be a familiar.
When a witch takes a familiar, they put some of their magick in the chosen animal, this does not do anything to the animal itself, it is just a bond between the witch and their familiar.
Familiars aren't bound to their witch partner, the animal and the witch have a trusting bond, not unlike that between a dog and it's owner.
Familiars are useful in rituals, most commonly used by Ceremonial Witches, but most witches take a familiar for security, having a familiar helps lower the damage a spell gone wrong can do, weather it be mental damage to the witch, or physical damage around them.
Spells are the basis of witch practice, and different spells are used by different witches.
Followers of Lucifer commonly use Earthly spells, plant growing, healing, and herbal spells, but they aren't limited to these spells, all witches can use all magick, certain spells are simply stronger for witches who follow certain deities.
Followers of Artemis also are stronger using healing spells, as well as sea magick, and animal magick.
Followers of Apollo are stronger with fire magick, and herbal magick.