HOW IT WORKS
When you click on collapse, part of the PastorsLine screen 'disappears'. When you click on expand, it reappears.
Here are some examples.
In the image below, we see three black panels.
If we click on collapse (turquoise box and arrow in image above), we see only two. The middle panel is 'gone'.
In the image below, there are two expand/collapse icons. In addition to the one we looked at above (turquoise box and arrow in image below), there is one on the right hand side of the screen (gold box and arrow in image below).
If we expand the screen, we will see details of the message we have chosen, In this case, the message chosen is Guest.
In the image below, there are two expand/collapse icons. One like we saw in Messages (turquoise box and arrow in image below). There is another one to the left of the persons name and thumbnail (gold box and arrow in image below).
Let's collapse both.
Now, both the middle and right black panels are 'gone'.
Additionally, you can permanently collapse the leftmost-hand panel to show only icons.
Click Profile --> Settings --> App Settings --> General --> Themes --> App Behavior --> First layer LHS Menu: Choose Minimal Mode.
It would then look like this: