How to add existing form as a child to a MDI parent Form??

I add a form which exists in another project (as a child) to a MDI parent form.But i can't get the child form after executing the MDI parent form.

Please help me....

Take a tool strip menu and in that tool strip menu you will get a button as new, just double click on that new button and write the code to call the child form as shown below and then run the project and then when you will click on the new button the child form will appear.

For Example in VB .NET suppose there is a child form named as preview_form .vb
Then the code for calling that child form is
Dim q as new Preview_form
q.show()