May I suggest that you consider using Soy templates instead of Velocity? Soy templates are used by the newer Atlassian products, and I believe the plan is to use them in new features added to JIRA and Confluence. In any case, Atlassian appears to be moving towards Soy and away from Velocity.
There is a suitable tutorial on using Soy templates in Confluence.
The documentation for Soy templates is published by Google.
Generally, you'll want to create a plugin to bundle all your code together and make it interact. Your other questions mention Confluence, so I'd start at https://developer.atlassian.com/display/CONFDEV/Confluence+Plugin+Guide
Even if this is not the right approach for your answer, the process of working through writing a plugin will teach you the basic stuff you need to understand to write code for Confluence, especially how java and velocity interact
Atlassian Summit is an excellent opportunity for in-person support, training, and networking.Learn more
Connect with like-minded Atlassian users at free events near you!Find a group
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no AUG chapters near you at the moment.Start an AUG