ClientManager Class
ClientManager works with the Android AccountManager class to manage user accounts. More importantly for apps, it provides access to RestClient instances through two methods:
getRestClient()peekRestClient()
The getRestClient() method asynchronously creates a RestClient instance for querying Salesforce data. Asynchronous in this case means that this method is intended for use on UI threads. The peekRestClient() method creates a RestClient instance synchronously, for use in non-UI contexts.
Once you get the RestClient instance, you can use it to send REST API calls to Salesforce.