I have a PeopleT and I created a GroupT.  Then I created a PeopleXGroupT following the steps you outlined with three fields: ID, PeopleID and GroupID.  Then the subform to show groups, which did not link automatically so I put in PeopleID and made it invisible.  It still did not link so when a box opened, I put in PeopleID as Master and Child forms as well as GroupID on the second line.  I slid the form into the PeopleF and when I selected a group, it entered the numbers on the junction table but the information does NOT show up on the Form.  Is this enough information for you to tell me what I am likely doing wrong?  Oh, I tried adding some data to the junction form and it "took" but not in the PeopleF.

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Reply from Alex Hedley:

Have you create a combo box for both People and Groups on the JunctionF.
Have you set a Default value for the People Combo so when it's on the PeopleF it defaults to the current person you're on?
The Link Master/Child Fields should take care of the filtering.