1: Capture the "active" window. (Link to definition/description of "active" window.)
2: Switch between all windows on the page.
3: Choose a capture window of any sized square or rectangle by left clicking once, drag the window to size, left click again.
4: Capture a freehand region by drag and multi-click.
5: Capture Full Screen.
6: Capture a "scrolling" window.
Re: How to use image Host Sites.
Informative information given step by step so easy to understood and utilise .All you would do here is press the browse/choose button which takes you to an upload window on your pc, choose an image, select it, and press upload. If you have a large digital image, it may take a while to upload.