To take a screenshot of the window you're viewing, you would press at the same time these keys: ( ALT and PRT SCR ) PRT SCR would most likely be above your Insert key.
Afterwards, open up the program Paint or any program that can edit images and such and press the keys: ( CTRL and V ) which would paste the image.
Do whatever you want to the image (ie. edit it, resize it, crop something out,) then save it somewhere like Desktop or into a folder of your choice.