In Windows 10.
Display a View that shows what we want to see. Copy a standard View and add columns to it if necessary. Expand the [Filename] column so that we can see the full file paths.
Press the Window Key+Shift+S to open the Windows "Snip & Sketch" application. Drag the crosshairs around the area you want to show to select it. Annotate the image if you wish or need to. Click the floppy disc icon to save the image to a file somewhere, in the png or jpg format. Give it a sensible name. Take note of where you saved it!
When you post, underneath the window you type in is a blue line "Attachments and other options". Click that.
Click the "Choose file" button, then navigate to the file you just saved and select it.
Make any note you want in the post, then Post it.
Done.
Or you can use the "Printscreen" or "Alt+Printscreen" buttons to save the screen or just an application window, respectively, to the Clipboard.
Then open Windows Paint and Paste the image into that, add stuff if you want, then save the image and attached it to a Post, as above.
Or there are lots of other applications to take screen images and save them as files. Basically, create an image file, then attached it to a Post in the forum.