The two-a-day is stage argot for vaudeville. It comes from the number of performances the actor “does,” for in vaudeville there are two shows every day, six or seven days a week.
Nevertheless, in this sense the novice needs no literary training. If he can see drama in real life and feels how it can be turned into a coherent, satisfying story, he can learn how to apply that story to the peculiar requirements of vaudeville. But no amount of instruction can supply this inborn ability. The writer himself must be the master of his fate, the captain of his own dramatic soul.
THE VAUDEVILLE STAGE AND ITS DIMENSIONS
To achieve success in any art the artist must know his tools and for what purposes they are designed. Furthermore, to achieve the highest success, he must know what he cannot do as well as what he can do with them.
The vaudeville stage—considered as a material thing—lends itself to only a few definite possibilities of use, and its scenery, lights and stage-effects constitute the box of tools the vaudeville writer has at his command.
The footlights are the equator of the theatre, separating the “front of the house,” or auditorium, from the “back of the house,” or stage. The frame through which the audience views the stage is the “proscenium arch.” Flat against the stage side of the arch run the “house curtain” and the asbestos curtain that are raised at the beginning and lowered at the end of the performance.
That portion of the stage which lies between the curving footlights and a line drawn between the bases of the proscenium arch is called the “apron.” The apron is very wide in old-fashioned theatres, but is seldom more than two or three feet wide in recently built houses.
Back of the proscenium arch—four feet or more behind it—you have noticed canvas-covered wings painted in neutral-toned draperies to harmonize with every sort of curtain, and you have noticed that they are pushed forward or drawn back as it is found necessary to widen or make narrow the stage opening. These first wings, called “tormentors,”  extend upward from the floor—anywhere from 18 to 25 feet,—to the “Grand Drapery” and “Working Drapery,” or first “border,” which extend and hang just in front of them across the stage and hide the stage-rigging from the audience. The space lying between the tormentors and a line drawn between the bases of the proscenium arch is called “One.”
 No one of the score I have asked for the origin of the word tormentor has been able to give it. They all say they have asked old-time stage-carpenters, but even they did not know.
It is in One that monologues, most “single acts”—that is, acts presented by one person—and many “two-acts”—acts requiring but two people—are played.