The usual suspects: You can either book a training at Progress for which you would need your local Progress sales rep or you can try to get into it yourself. If you are already familiar with OO languages like Java or C# the difference is not that big. As of OE10.1c the getting started section of the PDF documentation that comes with the product includes a book called Object-oriented programming which might be a good start for you. Other than that you can always benefit from the lively discussions on the different forums.
For my part I found it very easy to adopt my Java knowledge to OOABL programming.
Heavy Regards, RealHeavyDude.