To feature a product, you need to first, go to the product you want to feature. The best way to do this, is to find it on the public site. First make sure you are logged in. If you aren't, scroll up to the top of the site and click the login link on the top right, then surf back to the product and in the top towards the left, click edit product from the black admin bar at top:

Scroll down to the Marketplace Data module:

Click Yes under featured to feature this product then fill in the Start and End Dates:

To save this and feature the product, scroll up to the Publish module and click the Update button:

That's it! This product is now featured on the Marketplace.