First start by creating the screenshot. You can use this by either pressing "Print Screen" on your keyboard if you have it setup to use the snipping tool or press Shift + Windows Key + S. You will then be able to select the area of the screen you want to screenshot.
Once you have the screenshot copied to your clipboard, you can open the google chat window you would like to send the picture to and press CTRL + V to paste the image or Win + V to open your clipboard and then click on the image to paste it.
You can then type a message along with the picture
