This is the API details page. Use this page to modify the meta-data, plans, and policies for the API. There is no need to follow the tabs in order, but note that you will need to fill out a minimum amount of data before the API can be published to the Gateway. In particular, the Implementation and Plans tabs are important (more information below).
The 'Implementation' tab is where you go to configure the details of the real API being managed. This is where you tell apiman where the API is, so that we can actually invoke it at runtime.
The 'Definition' tab allows you to configure an optional API Definition document for your API. A API Definition is a detailed description of the capabilities of your API (operation names, http verbs, data models). For example, you might add a Swagger spec document as your API Definition.
The 'Plans' tab is used to configure which Plans (already defined in the Organization) are available when a Client App wishes to create an API Contract with this API. Optionally, an API can also be marked as "Public", which means that no API Contract is required (the API can be invoked without sending an API Key).
The 'Policies' tab is where you go if you wish to configure any policies that should be enforced for *all* requests to the API, regardless of which user, Client App, or Plan is being used. In other words, API-level policies.
The 'Contracts' tab will show a table of all Client Apps that have created API Contracts to this API. In other words, it shows all of the registered consumers of the API. Note that if the API is marked as "Public", this tab will likely be empty.
The 'Endpoint' tab will show you information about how to invoke the API once it is published to the API Gateway.
The 'Change Log' tab shows a history of all the changes made to the API. Essentially it is an audit log.