Create a form :
Right click your project and select "Add".."New Windows form"
Give it a sensible name (for example: "frmChatToUser", and then when you need to display it:
frmChatToUser chat = new frmChatToUser();
chat.Show();
or
frmChatToUser chat = new frmChatToUser();
chat.ShowDialog();
if you want it to prevent further activity in you main form until you have finished with the user.