No question, screenshots are your friend. There is a wealth of options for capturing screenshots on a Mac, with the two most common being Shift-Command-3 (entire screen) and Shift-Command-4 (area you specify with mouse). I like to have all images I capture/edit in a specific directory, the same directory that my ftp client points to upon startup.
Here is a defaults command (run from a terminal) that you can use to specify the location where to store screenshots:
defaults write com.apple.screencapture location path
The path setting must truly be the full path, that is, you cannot reference ~ for your home directory. If you would like to place screenshots in reference to your home directory, simply use the full path, such as /Users/John/Desktop/screenshots.
For the new path to take effect your best bet is to logout/login. Ive seen references to the following command as an alternative, however, this didnt work consistently for me:
You can also use the Property List Editor to set the your screencapture preferences. The file you need to edit is located here: ~/Library/Preferences/com.apple.screencapture.plist (use Finder to locate the file and double click to open).