You've got it right. You can move the arms in and out for wider or less wide frames.
And up and down for shorter arms. So you can ledge bigger and smaller frames on it.
You flip the top, with the frame lying on it upwards and then put the flat bit under your leg, thus the top bit is now in front of you and you can stitch without holding the frame.
The stitchmaster floor stand work at the same way, the frame won't fall off it is inclined a little more than in the picture, don't worry!
you can also use it with qsnap (as i do). Great find!