Q:

How do I call a method from another class within a listbox?

In my listbox form I want to make it possible to call a method from a class in a different folder. Here is what I thought I was meant to do:
public void ListBox_SelectedIndexChanged(object sender, EventArgs e)
{
    SharedClasses.Form.FormConsole newFormConsole = 
        new SharedClasses.Form.newFormConsole();
}

A:

You are creating a new instance of the FormConsole class, which I'm guessing is probably not what you wanted to do.
What you probably want to do is have the form that contains your ListBox have a reference to an existing instance of FormConsole. Then you can call methods on that instance.
So, somewhere in the class that contains your ListBox:
private FormConsole _myForm;

You can set that in the constructor for your class, or provide a getter and setter:
public FormConsole MyForm
{
    get { return _myForm; }
    set { _myForm = value; }
}
// and/or...
public ListBoxForm(FormConsole myForm) 
{
    MyForm = myForm;
}

Then you can call (public) methods on myForm:
public void ListBox_SelectedIndexChanged(object sender, EventArgs e)
{
    MyForm.MyMethod();
}

