session process in C#

You do:

//form1:
 public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        private void button1_Click(object sender, EventArgs e)
        {
            Form2 f2 = new Form2(textBox1.Text);
            f2.Show();
        }
    }
//form2:
    public partial class Form2 : Form
    {
        public Form2(string value)
        {
            InitializeComponent();
            textBox1.Text = value;
        }
    }