There are like thousand methods, the possibilities are nearly infinite. Circle is used for multiple stuff, to create space out of space and time, as well as protection.
Creating a circle:
There are two parts of creating a circle - imaginal and physical. You imagine the circle at the same time as you are creating it physically.
The simplest is the simple circle, just drawn by finger/wand/blade/etc. and imagined to be there, either in the air or on the ground. It isn't long lasting, but is clearly visible in spirit world. The physical part is missing here which is why it doesn't last long.
To make longer lasting one use a chalk, ash, salt or other material properly consecrated depending on your tradition. This circle lasts longer, effective for longer rituals and meditations, even overnight. You can also do it by drawing it in the sand, then you don't need to fill it.
Drawn circle allows for more enhancements, like the candles. Candles are easy to get and you can use prefered number - 4, 5, 7, 9, 12, 13, whatever number suits your need. Chalk circle also allows for more symbols around the circle, within, without, or by making two circles and drawing between them. Of course not only symbols but also words or names of power.
There are some really complex circles tutorials out there.
You can also buy or make a magic circle on a cloth, that can be reused many times, but don't forget that it needs to be "recharged," especially if not used for longer time.
