Heya! Don't worry, everyone has to start somewhere!
Everyone casts their circles differently, so you can find the way that best works for you, but this is basically how I do it:
Decide how much space I need, because you don't want to feel restricted and not have enough room to do what you need to do... Some people light candles for each quarter but I don't tend to do that. If you do want to do that then you could just use white candles for each corner, or if you want to use coloured candles, green to the north to represent earth, yellow to the east to represent air, red or orange to the south to represent fire, and blue in the west to represent water.
Basically what you need to do is call upon the elements. For example, I point my wand to the north and say "I call upon the elements of the north," then continue doing south, east and west. Although you can say more complex and elaborate things but this works for me.
When you finish, you usually start with the last element you called upon, so you would say something like "Thankyou elements of the west for attending this rite," or something like that, and continue until you finish with the north.
The purpose of a circle is so you can have a sacred space. Much like a church is used for religious worship and praying, a wiccan or pagan or witch can cast a circle to do magickal workings and the like. But before anyone leaves the circle it is important to open it again.
I hope this helped you, good luck on your path! If you would like some more information on casting circles, this is a good link
http://paganwiccan.about.com/od/wiccana ... Circle.htm blessed be

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