Help with AS3 and bitmap (confused w/ Tony Pa Tutorials)

In the new Tony Pa tutorials he has his characters being called upon from a bitmap tile sheet. How do you know which part of this sheet is being called upon with each instance? How do you know the size of this sheet? it wont let you copy and paste it out or right click - edit with (it says the file is not found).

Can anyone explain to me how this works?
Im not very familiar with actionscript 3

thank you,
Joey, thejoeknows.com