Form in C#

Question

hello, I'm new in C#.

I have a one small problem,  I have a class, where I have :

public void errRaise(string msg)

        {

           if (error == "")

           {

               error = msg;

           }

            // I would like to write on a label1 on Form1 a msg.

        } 

I know how to access label1 from Form1, but I dont know how to realize that in a class, please, help.