How are Tom, Daisy and Jordan careless people? What kind of things and creatures do they smash and then retreat back into their money?
Your question, of course, refers to one of the most famous quotes from the novel. Here are several examples of how they "smash" or destroy people and things without thought and then use their money to escape.
1. Jordan, while not necessarily a despicable character, is guilty of being thoughtless toward others and their possessions. She is not, however, as guilty as Tom and Daisy. Throughout the book, she cheats at golf, lies about damage she caused to someone else's car, and even excuses the horrendous deeds of others all because of her Old Money upbringing. Many seem to know that Jordan is a cheater and careless with others' things and hearts, but they excuse her because of her wealth and popularity. She even endangers Nick's life with her careless driving and nonchalantly brushes off his rebuke.
2. Tom is far guiltier of carelessly and intentionally smashing up others. Nick informs the reader that Tom cheated on his honeymoon and in the process wrecked a car and almost killed a woman who was not his wife in the accident. In that case, Tom has the money to pay off officials who might have charged him with a crime and to move away from any trouble he creates. Tom is also careless with Myrtle and George. He thinks nothing of destroying George's life while having an affair with Myrtle; he breaks Myrtle's nose without a thought and then uses his money to buy her gifts to appease her. Most significantly, Tom knows that Daisy is responsible for Myrtle's death, and yet he once again uses their money to move away from the "trouble" and lets more lives (Gatsby's and George's) be taken all in order to live seemingly carefree.
3. I would argue that Daisy is the most careless person in the novel. While Tom certainly causes much damage to others and their things, some of his stems from deliberate thought and action. Daisy, on the other hand, want so live in her protected, luxurious world without having to pay any consequences for her decisions or actions. In the end, she is the cause of the Wilsons' and Gatsby's deaths. She is careless with her daughter's well-being. In one considers her situation, he would see that Daisy brings a dangerous bootlegger into her daughter's life and exposes her to extremely selfish behavior on a regular basis. Finally, Daisy is responsible for Nick's disillusionment. When the novel opens, Nick possesses sympathy and a strange admiration for his cousin. But, as Gatsby progresses, Nick realizes that his cousin's careless behavior ruins things and lives, causing him to describe Tom and Daisy as he does in your quote. All of this seems not to bother Daisy because the novel ends with Tom and her using their money to build another house, travel away from their troubles, and maintain their place in society despite their destructive behavior.
Actually, Jordan Baker isn't included in the passage from the novel. After meeting Tom Buchanan on the street at the end of the story and hearing him talk about the events that had transpired when Wilson came to the Buchanans' home before killing Gatsby, Nick says this:
I couldn't forgive [Tom] or like him but I saw that what he had done was, to him, entirely justified. It was all very careless and confused. They were careless people, Tom and Daisy--they smashed up things and creatures and then retreated back into their money or their vast carelessness or whatever it was that kept them together, and let other people clean up the mess they had made . . . .
What Tom had done, of course, was give George Wilson precise directions to Gatsby house, knowing what the distraught Wilson intended to do.
What "things" do Tom and Daisy "smash up," separately and together? Gatsby's big beautiful car is literally "smashed up" with Daisy at the wheel. More significantly, Gatsby's dreams and Nick's naivete are destroyed by their actions. The reference to "creatures" suggests the human toll that resulted from their carelessness. Three people die in the novel: George Wilson, Myrtle Wilson, and Jay Gatsby. Their deaths resulted directly from their getting involved with Tom and Daisy Buchanan. After Myrtle dies, Gatsby is murdered, and Wilson commits suicide, the Buchanans pack up and slip away. It is Nick who is left to deal with the press and bury Gatsby. He is the one who has to "clean up the mess they had made."