You did not say, if you want to insert the "screen grab" into this forum?
Most Windows OS's have a program called, "Paint" .... just press Ctrl + Prt Scr buttons on the page you want to capture and then open Paint. Press Ctrl + V or click on the Paste button within the program.
Your screen capture, will now be pasted in the Paint program. Save the picture and upload it to a imgur.com. Once it's saved there, you highlight the direct link Url and copy and paste it.
Then you come back to the forum, and reply or create a new post and click on the Insert image button at the top. You then paste the url between the brackets, and it will be displayed on the forum.
Sorry if this is obvious, but there may be other people struggling with the same thing.