Posting a screen shot is a two-step process. First, you need to make an image of the thing that is showing on your screen that you want to show here. (In this case, the results screen from the ewido scan.) Second, is taking that image and uploading it here.
The first is done by a simple key sequence on the keyboard. If a window (the ewido results screen) is current on your display and you want to grab a copy of it, you press and hold the "Alt" key then hit the "Print Scrn" key. ("Alt" is next to the space bar. "Print Scrn" is a key on the top row at the right side of the keyboard - next to something called "Scroll Lock".)
That stores the image in memory and then you can paste it into Microsoft Paint, which most Windows PCs have available. Open Paint and simply choose the Edit menu's "Paste" option. That'll put the image snapshot you just took into the Paint application.
You can then save that as a file on your PC using the File menu, Save option. Saving as a JPG (jpeg) is probably best.
Posts here on Wilders can take an uploaded attachment using the "Manage Attachments" button that is below the window where you've typed your post text. It'll let you browse to the file you saved in Paint above and then Upload to your next post here.
Here is a thread that has more information on doing this: