The first error above is the clue:
Error 1 error C3145: '_serialPort' : global or static variable may not have managed type 'System::IO::Ports::SerialPort ^' d:\forms\rd\rd\Form1.h 32
You have declared a managed type as static which is illegal in C++/CLI, according to this message. You should make the variable a member of your class.
However, having read some of your other comments here I suspect that this subject is somewhat advanced for you. I would suggest you go back to your programming guides/ tutorials or other notes and try to get the whole concept of classes, objects and properties clear in your mind before attempting something like this.