You may have a key on your keyboard that says: Prt Scr
Click it and then open a program like MS Paint and paste it there.
To get a close shot of a particular item on your screen, press Prt Scr and alt at the same time.
Once you have them in MS Paint, click save as from the file menu, then save it to your C: documents > pictures.
When you want to post it here (for example), Type your reply, then scroll down to manage attachments. A window will open, then click browse for your screen shot picture, select it, by clicking on it, then open, then you'll be returned to the attachment window, click upload, then close window. When you post your reply, the attachment will be there. (It won't show in the preview post)
Good luck
Carolyn