Have you set your sub-form up correctly?
Each group is selected from the Combo Box in different records.

Combo Box seems to working fine. I can go to a customer record, then go to the sub-form combo box and select a group, then click on new record in the sub-form for that same customer and then select another group and so on. So I may have selected 5 groups for that one customer, they show up in the junction table, but the combo-box on the sub-form for that customer only shows me one group at a time, not a list of the groups as it shows at the 10m 35s of the video. I want to be able to see all the groups at once that I have selected for that customer.

Have you set the Subform to Continuous Forms?

I did have to change the Subform to continuous and that fixed it. Thank you for your help!