You do not attach ads to your hubs, this is done automatically. There are already ads on your hubs now, you just have not started getting your 60% share of the page impressions yet.
You need to enter your Adsense affiliate ID in your control panel. https://hubpages.com/my/affiliate
Once you click on the button, you will be prompted for information about the zip code and phone number you used to sign up for Adsense. Once submitted, you will get an email from Google with a confirmation link to click on. The affiliate ID should then appear in the Adsense panel on HubPages, which should change to "active," and your account will have been activated.
That is the procedure as I know it. If in doubt, check the Learning Center and FAQs available from the Help menu for additional information.