Starting with theme, which is the first thing revealed in "Cotton Blossom," the stevedore's introductory song with the dock girls expresses the theme of black oppression in white society:
Work while th' white folks play.
Loadin' those boats with th' bales of cotton. Gettin' no rest till the judgement day.
This is corroborated by the shots showing the segregation of white townspeople and black. Each group is equally excited and each group is distinctly segregated one from the other. Additionally, shots of animal romps help establish the lighthearted and excited part of the mood, which will stand in contrast to the mood of conflict that is introduced later, as in "Old Man River," in relations to the theme of black oppression and white superiority.
The song then establishes relationships between characters, including enmity between Steve and Pete. The inner traits of key characters are revealed through their brief dialogue exchanges and their characterizations while being introduced to the public, for example, the sullenness of Steve who is told, "Smile, darn ya. Smile!" The song introduces parts of the conflict. It is conflict that defines and drives plot. For example, the conflict between Steve and Julie is introduced: "If I ever catch that fella Pete talkin' to ya again, I'll break him in two." It also introduces the conflicts with Pete who starts a fight with Steve over Julia because Pete is angry Julia gave away Pete's gift broach. These begin the plot development.
In addition, the song establishes the nature of what the show boat is: it is a traveling source of entertainment that is excitedly received by its public. The show boat provides the setting and develops the mood (also called atmosphere) of tension and conflict in the midst of gaiety and excitement providing a dual mood..