2c8 Approve is a web app for those who only need to review, approve and leave feedback on your models. The focus of the web app is to involve process owners, managers, or other similar roles, without the need for a license in 2c8 Modeling Tool or 2c8 Lite.
If you already have 2c8 Modeling Tool or 2c8 Lite you automatically get access to 2c8 Approve to review and approve models. Those within your organization that don't have the need for 2c8 Modeling Tool or 2c8 Lite to create models, but should review or approve the models need a license for 2c8 Approve. Find more information about 2c8 Approve here.
In this FAQ you can read more about how to get a license for 2c8 Apps: I want an account for 2c8, what should I do?