Copy this exactly as shown and just place it in a little Notepad file or something and leave it on the desktop, whatever. Then whenever you find an image to post you put the address between the quote marks.
Note the space between "img" and "src"
Here's Google's image tag:
http://www.google.com/images/logo.gif
Placed between the quote marks, it looks thusly:
Copied and pasted exactly as shown, you'll see it....
Those instructions are for an image only. To have an image and some text, you need to learn to add paragraph tags at the end of each paragraph, and/or at the end of the image tag. A paragraph tag looks like this:
<p>
What about specifying the size, that's where I get lost?