now you write this code like:-
//In form 1 button or your contorl which you want to call form2
Form2 f2 = new Form2();
this.AddOwnedForm(f2);
f2.Show();
//now write code in form2 in load event or when you need to necessary to display form1 textbox value:-
Textbox t= (TextBox)this.Owner.Controls["TextBox1"]);
textbox2.text=t.text;
in above code textbox1 is the name of text box of form1 textbox. and textbox2 is name of form2 textbox.