FISTS, the International Morse Preservation Society, has a basic CW operators guide on their website that I think will answer your questions and more. The web address is: http://www.fists.org/basiccw.html
. The guide provides a brief summary of the proper way to conduct a QSO including the use of the procedural signals (or prosigns) like AR, KN, or AS that you might have heard. FISTS is a great organization if you're interested in CW, and FISTS operators are always willing to slow down and lend a helping hand for those new to the code. You can learn more about the organization through the link above.
Another resource you may want to check out can be found at http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=7749
and includes more detail on common abbreviations and the operating practicalities.
Good luck and welcome to CW.
73 - Will, AI4VE