Put succinctly, the Arrangement is similar to blocking in a more conventional production. The Arrangement (which I have kept in italics to differentiate it from the English ‘arrangement’ and to retain its specific meaning to a Brechtian theatre) is the symbolic placement of actors on stage to show onstage relationships as clearly as possible to the audience.
In a 'theatre of showing', everything on stage has a meaning. It is thus necessary to control placement and movement as carefully as possible. What is shown is often determined by the scenes’ Fabel. The Arrangement is effectively the Fabel made flesh.
A scene’s Arrangement should thus tell the scene’s contradictory story, noting turning points and the figures’ different relationships to the events. Ideally, the Arrangement is a series of clear tableaux that move logically from event to event, allowing the audience to follow the clear arc of the scene.