The second question is: When do I use what of these two?
When not specified, C++ is unmanaged C++, compiled to machine code. In unmanaged C++ you must manage memory allocation manually.
Managed C++ is a language invented by Microsoft, that compiles to bytecode run by the .NET Framework. It uses mostly the same syntax as C++ (hence the name) but is compiled in the same way as C# or VB.NET; basically only the syntax changes, e.g. using '->' to point to a member of an object (instead of '.' in C#), using '::' for namespaces, etc.
Managed C++ was made to ease transition from classic C++ to the .NET Framework. It is not intended to be used to start new projects (C# is preferred).