What is the best way to educate marketplace users on how to use your mobile app?

Best option is to make your mobile app so easy to use that you don't need to educate your users on how to use it. Use standard controls/navigation and strive to simplify, simplify, simplify!

Next best option is to educate your users right in the mobile app itself. Where users are getting stuck, try to get them unstuck, using graphics rather than text wherever possible, and using as few words as possible.

Last resort is to create documentation. If your mobile app is really complex, you might need an overview document to take your users through various tasks. But really, if it's that complex, you should look at simplifying (see 1) and taking users through the tast in the app itself (see 2).