The CTRL + PERIOD(.) + ENTER comes in handy when you type a class (or interface name) in the code editor but the
required namespace has not been referred by a using directive. When you place
the cursor on such a name and press that key combination, Visual Studio automatically
adds the using directive to the code file (if the relevant assembly has already
been referred in the project) or generates a code file for a new class by that
name (if the assembly has not been referred).
When you type an interface name in the base type list for a class, you can use CTRL + PERIOD(.) + ENTER to auto-generate stubbed implementations for all interface methods.