There is an enormous amount of information to be found on Sales Cloud on the interweb.
Here are a few public sources that help me personally and could be useful for everyone:
The official Sales Cloud product information
Anything from product information, implementation advise to managing your sales cloud subscriptions can be found here.
Sales Cloud Release Readiness
For every new release, Oracle is documenting what has changed in release documents, but also provides insight in how customers can take advantage of what has changed through a recorded presentations and demonstrations.
Sales Cloud Help
Once you have a Sales Cloud subscription, you definitely have to check out the online help. It is amazing how much information is available in the standard Oracle Sales Cloud help. From detailed information on product features to examples that might show how these features can be implemented.
Public version link: Sales Cloud Help (Click on sales to get just the Sales Cloud section of the Help)
And since the help can be customized, you can tailor the help further to exactly match your business processes.
Within Sales Cloud, the Application Composer is the tool to extend the application. Most of the extensibility work like adding custom objects, adding fields, defining layouts, creating workflows does not require any coding. For the rare exceptions, a scripting language called ‘groovy’, can be used to take the extensions a step further.
Oracle Enterprise Repository
The OERis a collection of links to rather technical documentation of Oracle Sales Cloud and other Oracle cloud applications based on the Fusion platform. Information like the Sales Cloud business process models and datamodel descriptions can be found here.