Forms :: Obtain Listbox Items From Another Form ?

I am using Visual Basic 2010 Express. I have 2 forms. A main form which does all the grunt work and then a small supporting form to get some additional user inputs.

Some program background...I am developing a program to characterize solid rocket motors based on test stand data for a hobby project. I load the time, thrust data into lists via a streamreader from a text box.

However, since the data is raw I would like for the user to select the "start" and "end" of the burn. I am currently trying to do it right after I load the data. As I read the data in, I just put it in the listbox of the supporting form as well. My main issue is, I need two values from the user. A start and end time. the index would probably be easiest, as I will rewrite the data list based on the time increment and delete everything before the first listbox selection and everything after the second selection. I can't get the values from the main form. I have exhaustively searched the internet trying to find something that I can apply. If someone could help with a framework on how to do this.

I understand how to get text from this text box on a different form, but this deals in variables and maybe setting up a class? I am having trouble communicating between the two forms.