The ideal Agile process is simple and repeatable. It's scope is high-level, but with specific goals. Scope is defined in a product roadmap. Goals are the features that add business value to the product. The process relies on similar patterns across levels, but with a greater focus on detail as a team gets closer to doing actual work. This does not mean that making that process work is easy. In fact, making an Agile process work requires commitment and discipline, but the steps within the process itself are simple.
The relative simplicity of an Agile process helps your organization move past the traditional project management focus on process and helps to put more emphasis on the interactions between team members towards deliverables and towards customer's needs and requests. After you have completed each step in the Agile process (such as completing a sprint, release, or product), your team should have a retrospective, discussing what went well and identifying areas of improvement.
Even though the basic structure of Agile is used by most organizations that use Agile, their approach to the details is rarely the same. There will be different names for a work item, work type, or backlog. There will be different relationships and orders of any work type. There will be different lengths of each phase within the lifecycle. There will be different approaches for how a work item is managed and defined in the backlog.
In order to make Agile work well in your organization, you need to constantly refine it and sometimes re-define it. The relationships of a work type, a work item, and a backlog is (in part) defined by your organization's work breakdown structure and (in part) defined by how your organization chooses to measure business value. In other words, the success of any Agile process has as much to do with an organization's commitment to Agile as it does to how an organization chooses the actual steps within the process.