Just call the 'Show' or 'ShowDialog' Method of the Form e.g.
Form2 f = new Form2();
f.ShowDialog();
Thats the code in c#, shouldn't be to hard to convert it in vb.
The difference between 'Show' and 'ShowDialog' is that 'ShowDialog' shows the called form modal. So you cant access the mainform as long as the called form isnt closed.
If you want to exchange data between the two forms you have to pass them in the constructor of 'Form2' or write some public properties.