Taking screenshots in Mac OSX uses Preview.
Inside Preview, you can use the menu to capture screens, but that's not very handy when you're working in other programs.
Luckily, there are some global shortcuts available that implement every way of capturing. As I always forget what they are, and I'm sure others forget this all the time as well, here's a short list.
|Cmd + Shift + 3||Capture the entire desktop, and save in on the desktop as PNG.|
|Cmd + Shift + Control + 3||Capture the entire desktop, and place it on the clipboard (instead of saved to the desktop).|
|Cmd + Shift + 4||Captures a portion of the desktop. The cursor will change into a crosshair, allowing you to select whatever you need. When the capture is completed, the capture is saved to desktop.|
|Cmd + Shift + Control + 4||Captures a portion of the desktop, but saves it to the clipboard instead of the desktop.|
|Cmd + Shift + 4 , space||Pressing the key combo, followed by space will change the cursor to a camera, and allows you to capture a single window by clicking on it.|
|Cmd + Shift + Control + 4 , space||Pressing this key combo, followed by space allows you to capture a single window, but rather than saving it to desktop, it is transferred to clipboard.|
Screenshots are saved on the desktop, and named after the date and time of the capture. Depending on your version of Mac OSX, the format is different: