Mac OS X Screen Shots:
Screen Shot to a Desktop file:
Command-Shift-4 - Drag to select copy region
Command-Shift-4-Space - Capture Window under cursor, then Click
Command-Shift-3 - Capture entire screen
If you want to capture a menu or pop-up, then use
Command-Shift-4-Space
NOTE: Preview can be used to annotate a Screen Shot with Circles, Arrows,
and Text to describe interesting points in the Screen Shot.
Screen Shot to Clipboard:
Command-Control-Shift-4 - Drag to select copy region
Command-Control-Shift-4-Space - Capture Window under cursor, then Click
Command-Control-Shift-3 - Capture entire screen
Now paste the clipboard into whatever a document that accepts graphics such as Mail, TextEdit, Preview, etc...
If you want a menu or pop-up captured in the Clipboard, then use
Command-Control-Shift-4-Space
Generally you can paste the image directly into your Mail app. Or some mail apps allow dragging the screen shot file into the mail message composition window. Depending on the mail application you use, it will either embed the image inline, or it will send it as an attachment. That is a function of the mail application you use and the method of adding the image to the mail message.