Yeah, some webforums and whatnot, to implant an image into the post one typically copies the desired image into the clipboard -- say, by lassoing it in Paint and invoking Copy -- and then hitting Ctrl-V to paste it directly into the body of the post. Dunno if the one you're dealing with is one of those, though.
When you download the image to your laptop make sure that it's a .jpg file or another common file format, it probably will be by default.
Make sure it's saved to the desktop.
If you want to send it in an email message open your email and find the insert button.
Place the cursor in your message where you want the image to appear, and navigate to the desktop, select the image and click OK or whatever your email requires.
The picture should appear in your message.
If you are not doing this with email, just select the photo on the Desktop and click Copy, then go to your document and place the cursor and right click and select Paste.
If you need to size the image, your email will probably let you select a size, if you are pasting it into a word document you can size in Paint or some other image editing software on in Word it will let you drag it to the size you want.