Just after the curtain goes up, Tom gives us some brief details concerning each of the characters— including his mother, Amanda. But it's not until Amanda appears on stage that we get a good idea as to what kind of person she is. Straight away, we can see that she's a bit bossy, nagging Tom to eat his food in what she considers to be the correct manner. This is clearly a woman who exerts a great deal of control over her children by infantilizing them: trying her level best to keep them in a state of arrested development. By giving Tom lessons in etiquette, Amanda undoubtedly means well, but we can understand why Tom snaps at her ceaseless fussing.
Unlike her brother, Tom, the docile Laura is not in a position to resist her mother's constant nagging. She meekly does as she's told, practicing her shorthand and typing in the living room of the cramped apartment, in preparation for the vast hordes of gentleman callers that are supposedly going to turn up. Laura knows full well that this isn't going to happen, but Amanda's resolute that it will.
This reveals another one of Amanda's important character traits: her self-delusion. She's forever trapped in a fantasy world—in a dim and distant past when numerous eligible young gentlemen would beat a path to her door. She reminisces fondly about those long lost days, even though Tom and Laura must've heard all of her anecdotes at least a hundred times.