Casting a circle is simply a precaution for when you cast spells.
There is no real way to cast one, it’s different for everyone.
The main idea is to form a circle with a wand and simply call upon protection, at least, that’s how I do it.
Some people typically call upon the elements, ask their spirit guides for protection, or even the deities they worship for help. But the most typical method is the elements, starting in the direction of north and moving clockwise, imagining a complete ring or circle protecting you, and ask the elements or whoever to aid in protection.
And to close the circle start at north and go counterclockwise, picturing the line being absorbed back into you while thanking whoever you called out to.
Also, the circle should be big enough that encompasses your work station, and gives you enough space to move around in comfortably.
A circle is not an absolute necessity, unless it is part of the process in the tradition you follow or prefer.
Whether one begins at the east or the north, again, is a matter of tradition, and not mandatory.
Whether any entity or entities are called, is a matter of belief and tradition.
Any tools used falls under the same answer.
The point, Weralinax, is that anyone who gives you answers as absolutes without knowing which tradition you follow (if any), is answering according to their own beliefs. It certainly does not make them wrong in the least; they are answering from their own perspective.
There is nothing wrong with using a wand, if you so choose. A wand, most broadly, is used to direct energy and intent. It is simply a pointing device, representative of the element fire in some traditions. Some traditions use a ritual knife for the purpose. Some may choose to walk a perimeter, and some may choose to simply point.
Starting in the north or east comes down to the way the cardinal directions are interpreted by a given tradition. Some consider East the place to start, being the direction of sunrise, and the beginning of a new day. Some consider North the starting place, as one of the two fixed cardinal directions, the primary directional reference on most maps (especially in the Northern hemisphere), and the direction of the North Star, Polaris, which seems to be in a fixed place in the sky.
It is at least somewhat widely accepted that the direction the circle is created is important, with clockwise being for invoking energy into the circle, and counter-clockwise being for banishing energies. Similar can be said of visual representations of the elements at the quarters being traced in mid-air, such as with the Lesser Pentagram rituals, or the Greater Hexagram rituals from the Golden Dawn tradition. Similar is also used, by the way, while mixing ingredients in some spells. But again, it does come down to tradition, though it's 'broadly' accepted.
Any entities, spirits, representatives of the elements, etc., which are called, are very much determined by tradition. Some will simply invite 'spirits of' a given direction or element, while some use names they have learned. Some are named individually, while some are listed with attributes as well. I have not studied very widely, but I do know in traditions which borrow from the Golden Dawn tradition, that the elements are as follows (beginning in the east, moving clockwise):
East is Air, represented primarily by yellow;
South is Fire, represented primarily in red;
West is Water, of course being blue;
North is Earth, represented by green or brown most often.
If you choose to cast a circle, I would suggest doing a bit of research on some of the wider correspondences of the elements, or consulting whichever tradition you are studying, or currently at least feel closest with. At the very least, you can find an actual guide about casting a circle.
A circle has a direct purpose, which changes in different traditions. But most widely, it is used to separate a space for its specific purpose, for the duration of the working. Some may choose to banish prior, or use the casting of the circle to banish. Either way, it is a means of creating a sacred space, or a step in preparing a space already declared sacred. It's sort of a bubble of sorts. Some people consider it protection, and cast their circle as a barrier, while some cast theirs as a door, open to whichever energies or entities they may be calling. Again, this varies by tradition and personal belief.
In some traditions, a circle cannot be crossed once cast, until it is dissolved or removed at the end of a ritual. Some traditions with group rituals may have a way to compromise this, creating a bit of a gate if someone must leave. But it is generally advised to take care of any bodily needs which might impede the work at hand. Once the working is done, the circle is dissolved, or whatever method is used in the case of the practitioner, and things can resume.
