The latest versions of OJS and OCS support interoperability with the popular PayPal online payment system. It will allow you to collect a variety of registration, author submission, donation, and other fees securely and online -- without your users needing to have a PayPal account at all.
To get started, take a look at the document "Using PayPal for OJS and OCS Payments". It outlines the steps required to create a PayPal account and configure OJS and OCS to collect secure online payments.
The Scientific Dissemination Unit of the International Centre for Theoretical Physics has released a free online book, Science Dissemination Using Open Access. It includes sections from various PKP documents, as well as many others.
It provides a single source for anyone new to open access issues, as well as outlining some important practical steps in moving forward (such as using OJS!).
The PKP Team has created a new document specific to OCS and OJS: The OxS Quick Reference.
This reference document covers common system tasks for both OCS and OJS. It includes instructions on: installing and configuring the software on a server; publishing content; and practicing necessary server administration tasks (making backups, upgrading, troubleshooting, etc.). It also includes additional material useful for developers who are looking to make additions and modifications to the code.
I'm happy to report another addition to our PKP documentation: Translating OJS and OCS. It's available in HTML and PDF. It covers installing and maintaining language packs for both OJS and OCS, and also covers how to make your own translation.