If i have created two form, the first form is the main form and another is just a secondary form. After i click on the login button, then another form will be shown up. Can anybody help me how is the coding look like?

is the coding look like the below:

Form childfrm = new Form2();
childfrm.MdiParent = this;
childfrm.Show();

May I Know You?

It depends how you want to show the second form. I'm guessing if it's a login dialog then you don't want the application to proceed until after a successful login.

Try... Kep.