You make a custom group so on the sidebar there's a heading of friends and you click on edit custom groups and then there will be a few pre-made ones and then at the bottom it will say new, you can click on that, name the custom (it usually helps to name the custom the person's name or journal name so later you're not confused), and then pick who is on the group by selecting their journal from the not in group section and clicking the >> button to put it in the in group row and then once you're satisfied with that hit save changes. Then when you go to post an entry it will have "show this entry to:" at the bottom, go to custom... and then all of your customs pop up at the bottom, you check the one you want and then voila, you're all set. Sorry if any of this is confusing/not clear.