I'll start off by validating your struggle. The navigation for the SDK docs is less than optimal. The good news is we're working on several key updates to the dev center for early next year that should improve the ease of navigation and streamline the overall API/SDK documentation experience.
The SDKs are broken down into the same categories as the API docs found here: https://developer.mypurecloud.com/api/rest/v2/. Each category in the left-hand navigation on that page has an API class in the SDK. So the Conversations category has a ConversationsApi class, Users has UsersApi, etc. There are links to each category class on every page of the docs, but they're mixed in with all of the model classes as well. The easiest way to navigate to those pages in the SDK docs is to use your browser's in-page search feature to find the API class in the navigation.