1. Whole desktop screenshot- This screenshot will cover everything on your desktop, meaning everything that you see on your screen will be included. Open all programs, applications, etc. that are to be included in the screenshot. Once you are ready, press and hold Command, Shift, and the number 3 key, then release simultaneously once all 3 are held. Check your desktop for a new .png file. It will have the title Screen Shot.
2. Specific desktop area screenshot- This screenshot is also of your desktop, but only a part of it, which is of your choosing. Open the item or items you wish to have a screenshot of. When you are ready, press and hold Command, Shift, and the number 4 key, then release them simultaneously. You will see crosshairs where your cursor was, allowing you to size a specific portion of the desktop. Left click your mouse and drag over the desired portion of the desktop. Let go of the mouse button when ready. You should see a .png file of the screenshot.
3. Window screenshot- This is a screenshot that is taken of just one window that is open. Open the desired window, then press Command, Shift, and the number 4 key and then simultaneously release. Press the spacebar and then mouse over the open window and left click on the window once. You should notice a new .png file of the screenshot taken.