Although I am currently a thelemic magician, I started out in "Magick" through a friend of mind who initiated me into Gardnerian Wicca.
Learning about circle casting is a wonderful way to begin your path into any form of magick discipline. The circle is symbolic of your universe as well as a representation of the entire cosmos/creation. You could see throughout many cultures the use of the circle, particularly through what are known as "Mandalas".
Creating your own personal Mandala would be great as a start in understanding the circle, but you could also begin to learn about real "visualization" of astral circles.
All circle casting is performed within your available room/bedroom/garage/etc. You actually do not need any special tools (later in your journey you can start finding a good wand from a special tree like I did many years ago and use it in casting a circle). For now just use your index finger and, going clockwise, created through sheer visual/mental imagination a blue flaming line all around you.
Learn to keep this circle as vibrant and flaming blue as possible. The key here is imagination and your will. As you "draw" your circle state your intention for drawing it as you move clockwise.
Another way to work with a circle is to simply make one of your own physically. You could purchase a drop=cloth from home depot used for painting interiors and simply draw a black circle with all the symbols you want (its your circle so make it as original as possible). This would be the best alternative if you are beginning. this way you would condition your mind/sub-conscience into understanding and accepting the validity of the circle as a true magickal barrier.
As to Spell Casting I will write up a separate post about how to really make spells work instead of just going through the motions. First get a grip on circle casting (if witchcraft/wicca is what you are dealing with)as well as understanding what the elements are in nature and how to use them within your "circle"