Although they can be structured differently, memory plays usually begin with a recollection, a monologue delivered by the main character. The protagonist remembers an important moment in his or her life, and then the story of the past unfolds on stage.
In some memory plays, the narrator/protagonist comments throughout the play. (Think of the adult Ralphie in A Christmas Story). In other memory plays, such as the Tennessee Williams classic The Glass Menagerie, the protagonist narrates at the beginning, becomes a fully involved character during the bulk of the play, and then segues back to the role of the narrator to offer final reflections about his memory.