Here at OSTraining we've given significant coverage to Drupal Commerce. You can watch a video class with nearly 30 lessons and download a book, "Building E-commerce Sites with Drupal Commerce".

However, Drupal Commerce is an enterprise-quality solution and a good number of OSTraining members have asked for simpler solutions.

For those members, we often recommend the Payment module, which makes it easy to add e-commerce fields to your content.

Payment supports about half-a-dozen gateways (PayPal, Stripe, iDEAL, Authorize.net, Ogone, Rabo OmniKassa).

In this tutorial, we'll show you how to use the Payment module, together with PayPal.