You're not quite done yet. It's in your media library now, but you want to make sure to link it to YOUR affiliate link so you get credit for any sales made through the ad on your page.

Click the "link" button.

Add your own affiliate link to the destination URL window. I prefer to click "Open link in a new window/tab" box, because I don't want to direct traffic away from my site entirely. If they don't buy at the site I linked to, it should be easy for them to come back to me for more details or to comparison shop with similar companies I tell them about on my site.