You are asking very basic questions, all of which are answered if you watch a couple of mapping tutorials.
I like these ones, go watch all 4 and if you still have problems, come ask your question again.
Lolto's mapping tutorials:
Episode 1: Basic Introduction
Part 1:
http://www.youtube.com/watch?v=Gb7wjLqA_o8&feature=relatedPart 2:
http://www.youtube.com/watch?v=drEwL5YJfDs&feature=channelPart 3:
http://www.youtube.com/watch?v=rjHMaW9w0Lc&feature=relatedPart 4:
http://www.youtube.com/watch?v=wCL3kbGScko&feature=related