How to create a Confluence page with Simple Groovy script usage with onDemand Confluence ?

Hi,

As part of evaluation, we want to check how we can create the forms

 for small document collection applications ensuring the data can be validated for non unique etc. 

I tried analyzing the documentation, but was not clear on 

1. If Groovy is external or inbuilt plugin.
2. At some documentation it is mentioned that we can not install any third party plugin (groovy plugin !) 
3. How to create a simple page with dynamic content coming from Groovy.

When I try to use "Other Macro" on the page, I do not find groovy macro as part of it.

Kindly answer or point to the appropriate documentation. Will appreciate assistance on the same.