A good abstraction shouldn't require you to understand what's going on beneath.
Abstractions are good because they allow you to focus on what's important for your application, as well as enforce seperation of logic.
For example, an application that writes text files should not know anything about how the underlying file system works.  The file system abstraction forces this.  So that if the underlying file system is changed, the application should still work.
For personal knowledge, it's difficult to say.  Be aware that implementations change, so even if you've learnt how they worked under the hood, it's not necessarily the same all the time.