Hi Matthias,
There is no global server side caching of entire pages, there is a setting in page settings to allow client side caching. Some features like the main Html Content feature allow caching of server side partial page output. This is done from the feature instance settings on the General tab, if the feature supports it.
Features that do postback generally cannot be cached because this causes viewstate errors when a cached copy is posted back and the viewstate is not valid for the current postback request. Also things that are personalized or where content varies by roles cannot be cached easily as it would require a separate cached copy per variation.
Are you having actual performance problems that you are wanting to try and solve with caching?
Unless you have a specific performance issue you are trying to solve I recommend leave caching settings alone. Caching uses server memory which in most hosting situations is the most precious resource of all. If some content is very expensive to build from the database, caching can be a solution to reduce database load (if it is identified as a bottleneck) but if you cache things without good reason and without having a lot of memory available it can actually hurt performance. Most hosts put tight limits on the memory available to a web application and if the the app uses more than a set threshold it will recycle the application to free up the memory. An app that recycles constantly will perform badly.
Best,
Joe