This doc guides you through getting the process of enabling and creating Nintex Forms.
These are applicable to both Nintex Forms 2013 and Nintex Forms 2010.
A few additional tips
Want to know what Browsers Nintex Forms support?
New to Nintex and looking for additional resources for learning how to use Nintex products, or want to brush up on some features? Head to the Nintex Learning Center to find more training resources, and allow you to earn Nintex certifications.
I really want to be able to add a link to a Nintex form to a task for easier access for approvals. This is possible with SharePoint designer and InfoPath and should be possible with Nintex. At the very least should be able show links to Workflow tasks on a linked webpart.