how to call a function in classlibrary

You need to do the following :

1) Reference the class library in your main project.
2) create an object of the type you need.
2') in case of static classes you don't need the above.
3) call the method you need.

public class classlib
{
   public void Method1()
   {
   }
   
   public static void Method2()
   {
   }
}

public class Main()
{
    classlib myClass = new classlib();
    
    myClass.Method1(); // call normal


    classlib.Method2(); // static method call
    

}