I'm struggling to understand the visibility of objects and their properties & methods in .Net, can anyone assist?

For Example;

I have a simple project with two forms "MainForm" and "SubForm", there is a button on the MainForm that calls the SubForm.

If I was in VFP I would expect the subform to be able to see the properties and methods of the MainForm, EG. MainForm.MyProperty etc. but in .Net although I can see MainForm and all base properties I can't see any of my custom ones.

Code looks like this

namespace WindowsTestApplication
{
    public partial class MainForm : Form
    {
        public int publicInt = 0;
        private string privateString = "Hello";

        public MainForm()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            Form oSubForm = new Form();
            oSubForm.Show();
        }
    }
}

namespace WindowsTestApplication
{
    public partial class SubForm : Form
    {
        public SubForm()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            // Want to reference MainForm here.
        }
    }
}

Thought in the above I would be able to see 'publicInt' but not see 'privateString', but I can't see either.

Gary.