The "marks" in Lanley's con scheme were towns that were in possession of large amounts of money. Lanley would visit a town and make a sales pitch for his monorails to encourage the townspeople to purchase one. After the town bought the monorail, Lanley would open a monorail conductors' training school to hire a conductor, which was really a farce and provided very little in the way of actual training. Lanley would either select a random student or the least qualified in the class to be the conductor (his exact decision-making method isn't known).
After the monorail was built and a conductor was selected, Lanley would set up a huge opening ceremony with a celebrity presiding, then leave (with the town's money) while everyone's attention was focused on the opening ceremony and the celebrity. The monorail (due to shoddy materials) would typically crash on its first run, causing loss of life and extensive property damage, and leaving the town financially ruined. Meanwhile, Lanley would go on a resort vacation bought and paid for with the "mark" town's money.
Lyle Lanley: Well, sir, there's nothing on earth like a genuine, bona fide, electrified, six-car Monorail! What'd I say?
Lanley: What's it called?
Patty & Selma: Monorail!
Lanley: That's right! Monorail! [crowd chants 'Monorail']
Miss Hoover: I hear those things are awfully loud... Lanley: It glides as softly as a cloud.
Apu: Is there a chance the track could bend?
Lanley: Not on your life, my Hindu friend.
Barney: What about us brain-dead slobs?
Lanley: You'll be given cushy jobs.
Abe: Were you sent here by the devil?
Lanley: No, good sir, I'm on the level.
Wiggum: The ring came off my pudding can.
Lanley: Take my pen knife, my good man. I swear it's Springfield's only choice. Throw up your hands and raise your voice!
Lanley: What's it called?
Lanley: Once again...
Marge: But Main Street's still all cracked and broken...
Bart: Sorry, Mom, the mob has spoken!
All: Monorail! Monorail! Monorail! [big finish] Monorail!
Homer: Mono... D'oh!
In Springfield, Lyle Lanley interrupted a town meeting when the people were trying to decide how to spend $3,000,000 the town had collected in fines from Mr. Burns, who had carelessly left nuclear waste inside a tree. The town was on the verge of voting to use the money to repair Main Street (which was cracked and broken) when Lanley successfully made his sales pitch for the monorail. At the conductors' training school, Lanley chose Homer Simpson to be the conductor due to apparently being competent for the job as he (Lanley) walked out the door on the last day of class. The monorail opening ceremony featured celebrity guest Leonard Nimoy, who wowed the townspeople by joking that the monorail could do at least Warp Five. After the first run started, the monorail's throttle inevitably broke and its brakes failed, leaving the monorail speeding out of control. Monorail conductor Homer saved the day, however. He took the "M" from the "Monorail" sign and used it as an improvised anchor, embedding it in a giant metal donut atop a donut shop and stopping the monorail without serious injury to the passengers.
Lanley, meanwhile, boarded a plane for Tahiti, looking forward to his next vacation. His plans went awry, however, when his flight made an unscheduled stop in North Haverbrook, one of his previous monorail "mark" towns. Apparently alerted to Lanley's presence, a crowd of locals boarded the plane and attacked him, at least beating him up as Lanley was heard screaming and the plane was seen rocking back and forth.
-  Lyle Lanley at the Simpsons Wiki