With the risk of repeating what Kystar said...research on the net and read some books, make comparisons and see whatever appeals to you! I don't cast circles but I highly suggest doing the circles as a form of protection because you're starting out. The cermony also focuses your energy and thoughts.
way to cast a circle would be:
prepare yourself by having a bath and put on some special robes or clean clothes, possibly white, but any colour that you feel is important
starting at the east, draw a circle clockwise in salt/chalk/pebbles, imagine energy flowing out of your hands or whatever tool you're using as you cast it. The 'circle' is often imagined more of a sphere reaching over you, the circle you've marked on the floor as the circumference
set up something that represents each of the elements in the four corners (there's a thread on this forum on how you designate elements to directions) for example an incense stick, a candle, a dish of water, a dish of earth.
clockwise ask each of the elemental guardians in turn to come and protect the circle (again, personally I would start with East and finish at North), lighting symbol or placing hands over. They will now 'inhabit' your symbol
after you've done what you wanted to do, thank any gods you've worked with, thank each of the elements in turn and be aware of them leaving, going anticlockwise extinguishing flames as you go. Erase the chalk or pick up the stones in an anticlockwise direction.
I'd keep a notebook as well to write down different ideas and later to be able to compare what you've done.