Familiars

A familiar is a supernatural entity which bonds with a witch and lives with them throughout the course of their life. They take on the form of an animal(and only animals) and can live to be several hundred years old. Sometimes a familiar will bond with multiple witches over the course of its lifetime, but never more than one at a time.

Functionally, familiars are a lot like pets. The witch cares for it, and it lives alongside its witch. They often name themselves, and they don't like being coddled. Many take offense to the term 'pet.' They can communicate with their witch, and only their witch, and they often follow the witch around. They're mostly for companionship, though they can, on occasion, be persuaded to assist the witch with their tasks.

Familiars can take on the form of any animal. 

FAMILIARS ARE NOT ALLOWED FOR FRESHMEN AT ROXFIELD. The other dorms are allowed to have them. 

Wands

Wands are fairly straightforward. They aren't inherently magical items in themselves, and instead act as conductors for a witch's magic. They aren't necessary for all forms of magic, and most magic(with the exception of a lot of ritual magic) can be performed wandless with a little bit of practice.

Wands are made of wood, and they often contain either silver or iron cores. Silver is better quality, but iron in cheaper. In terms of wood, most any type of tree will work, but the tree must be at least 100 years old and the wand wood must be unbroken. 

Some people claim that painting certain patterns or carving wands into certain shapes make them more effective, but this is largely untrue. With the exception of runes(which are a form of magic anyways) wands don't hold magical ability in this world, but simply channel a witch's natural ability. 

Witch Law

There is no 'secret society' of witches--or at least, not in the sense that one might imagine. They're somewhat of a community, and there are independent, witch-run organizations, such as magical newspapers and colleges, or even businesses, if you know where to look. There is a Council in each country, made up of varying amounts of witches(the U.S. has one witch for each state) and they have the power to form a police department, regulate magic use, and the like. As a rule, though, they wield their power sparingly, meeting for only seven days a year, and they collect the absolute minimum amount of taxes needed to continue running. There is an expected sense of secrecy surrounding one's status as a witch, but that secrecy is not enforced. If you get caught, The Council is unlikely to protect you and in fact, the Salem Witch Trials is the only recorded instance of The American Council ever stepping in to prevent humans from slaughtering witches.