To get started, you'll want to log in to your AdSense account, then click on the Ad Settings tab. The first section is labelled "Ad Type" and you should see this:
Ad Type selector including AdSense for Feeds
Click on the new "AdSense for feeds unit" and select the type of Weblog program you're running out of the choices (Blogger or Movable Type/Typepad).
In the "Your AdSense code" box you'll see the code you should add to your feed, but don't do that yet. You want to create a unique channel for your RSS advertising first, so you can track impressions and click thru rate. In the middle of this same page, there's a section that lets you work with channels:
Configuring channels for your AdSense for Feeds ads
Click on "manage channels", then type in the name of the channel you want to create (I used "RSS Feed") and click "create new channel". It'll look like this:
Create a Unique Channel for your RSS Ads
Now, click on the "Continue to Ad Layout >>" link at the bottom of the Channels page and you'll be back to your original page, but now you can select the new channel!
Now in the "Your AdSense code" box is a bunch of obscure looking HTML that you'll want to copy and paste into your RSS template. Let's look at that part next.
If your browser supports tabs, I'd recommend that you create a new tab before you move to your Weblog configuration page, so you can flip back to the Google information with ease.
If your Movable Type configuration is like mine, you'll have a "Templates" link on the left side of the main page, which, once you click on, will reveal all your templates, including both an RSS 0.91 and RSS 1.0 index page.
Click on the first one, "index.xml", and you'll be looking at your template, which is about as scary as a file gets in the blogging world!
Somewhere in that jumble is a code section that looks like this:
<$MTEntryExcerpt encode_xml="1"$>
Position your cursor just before the tag, insert a few blank lines, then back up one and paste in the code from the Google AdSense page. Click on SAVE then click on the bottom REBUILD button and you'll be able to quickly rebuild just the target file.
You'll want to do a similar thing to the "index.rdf" file too. The XML that's shown therein is a wee bit different, but the same basic technique will apply.
Now, to test it, subscribe to your RSS feed from within you favorite RSS Aggregator (I like NewsGator Online, personally). Your ads should show up pretty much instantly!
Now don't forget to read my Best Practices: AdSense for Feeds and AdSense for Feeds: Any Risks? before you go too much further.
Congratulations, you now have adverts in your RSS feed. Good luck with them. Me? I think you should only have adverts in full text feeds, as I talk about at length in the following article about Ads in RSS Feeds? Corrupting the idea of information syndication.