A circle in magick has many uses. It is used for protection, as a barrier or as a gate to another dimensions. It is basically the place where your energies will be raised. There are many rituals to open a circle from very simple to more complex. The basic circle opening is to use your wand or the index finger and draw a circle in the air arround you while you visualize a white (Colour may vary from ritual to ritual) light. It ussually contains words that you have to speak like
"The circle is now open but not broken" and when you finish "The circle is now closed/broken".
As magick circles are mostly used in witchcraft, for wicca and pagan religions, you may wish to take advices from Lark, I guesed she is more experienced with them. Anyway I offer you this site to read the procedure: http://suite101.com/article/how-to-open-a-wiccan-circle-a71600
A symbol could be anything. Pentagram? If it is wicca then the moon of the triple goddess?