Just create a new Form variable, initialize it, load a layout and then show it:
Dim newForm As Form
newForm.Initialize("newForm", 100,100)
newForm.RootPane.LoadLayout("newFormLayout")
newForm.Show
If you take a look at the template code in a UI app, all those steps are performed with MainForm, with the exception of initialization, in Process_Globals() and AppStart().
You can create the newFormLayout with the Designer. The above code can appear in your Main module; no need to create a new module for it as in B4A and Activities. You can, if you want, make a Form a member of a class (click Project>Add New Module>Class Module), but that isn't necessary. I would recommend putting newForm's event subs and MainForm's event subs in separate regions for purposes of code readability:
#Region MainFormEvents
'MainForm events
#End Region
#Region newFormEvents
'newForm events
#End Region
but again, it's not necessary.