There appears to be little documentation on the net for the most simple part of creating VSTO Add-ins.
Once you have created your ribbon and your controls on it, you may want to use them to launch your app’s forms. This really is simple, looking at the snippet below, presuming you have a command button named cmdLaunch on your ribbon:
Public Class Ribbon1
Private Sub cmdLaunch_Click(ByVal sender As System.Object, ByVal e As Microsoft.Office.Tools.Ribbon.RibbonControlEventArgs) Handles cmdLaunch.Click
Dim dlg As myForm = New myForm
This will launch your form in ‘Dialog’ mode