Plug-In with an ipt

[Freude1976]

I'm slowly teaching myself Visual Basic and working through tutorials creating various plug ins.  The tutorials are dealing with assemblies and I can see how the code accesses and assembly file but cannot figure out how to access an ipt.  For instance, I would like to create a form that builds a block with user input for, length, width and hieght...how do I get the form to load into that ipt.  I must just be missing something...again I can see from the tutorial I was doing how the form accesess the assembly file when I build it but can't get the current project I'm working on to access the ipt...  Thanks, and hope this makes sense.