You could always use Grab, Apple Macs built in screen capture software but I will tell you how to print screen in seconds, even capture screen images ready to go straight into you blog or powerpoint presentation, already cropped and re sized without the need to use a program such as Adobe Photoshop.
Ok, first method. Hold SHIFT + COMMAND + 3 to print the entire screen, this will automatically place a high .png file on your desktop with a generic name.
Second method, SHIFT + COMMAND + 4 provides you with a set of cross hairs to select your desired workspace. Click and hold at the top left of the part of the screen you wish to capture and then drag diagonally down until all of the area is highlighted, release the mouse and the image will be generated and saved to your desktop.
If you change your mind press escape to remove the cross hairs.
Be sure to name the image in a way the the search engines can read what it is, for example My_Screen_Grab.jpg
Insert the image into your blog, web page etc and have a brew with the time you just saved faffing about with picture editing programs.