There are so many ways to "Call a Circle" and there are many variations of a Circle that are practiced in Wicca. I will only be speaking of different circles found in Wicca, Calling a circle is an entirely different blog. :)
You've got a circle around a Star which it the Pentagram that I have discussed previously. A circle around a Pentagram means it's a closed pentagram and the elements within it is being controlled in some ways. (Since Wiccan's use their practice as some form of "control" in their lives, it only makes sense that their symbol reflects humanity in control)
The image of a Snake eating his own tail is an old Chinese proverb within its self. It shows Life and Death, very much like the circle of life but more disturbing, I think. Snake is alive, snake starts eating himself, snake begins where he ends. A lot of Wiccans believe not in an afterlife, but in reincarnation. (Reincarnation is when your soul is transformed or transplanted into a new being and a new life, trying to accomplish what your soul needs to do to ultimately purify its self and in time, be welcomed to "The Great Meadow")
When a Wiccan casts a circle, it isn't just a circle but a Sphere of Protection for the one in the middle (or surrounding) it. The circle is meant to protect everyone involved and dispel any negativity within the Circle. In Hocus Pocus you saw the older brother put a circle of salt around his younger sister to ward off evil spirits. Salt is often used in spells that are "heavy" on magic or if the caster feels they need an extra bit of protection, although Candles are reflected in the same way, as a ward against anything that might want to "Piggyback" the spell.
So basically, the idea of a circle is what goes around comes around. What lives, also dies. What dies can also live again. He who suffers can once again feel happiness. And all of that fun stuff.
There are Circles everywhere in life. When I think of a circle I think of a full moon, the highest peak of magical thinking... or the craziest time for the general public.... the highest tides and the brightest nights. I'm kind of obsessed with circles, you could say. I see them everywhere and a heed them when it's needed.
When you think of a circle, what do you see?