How does Iago make Otello suspicious of Desdemona and Cassio?

In Giuseppe Verdi’s Otello, Iago systematically manipulates Otello’s emotions through psychological suggestion and the fabrication of physical evidence to incite his jealousy.1

Iago’s strategy includes:

• Planting Doubt: Iago stages encounters to make it appear that Desdemona and Cassio are behaving guiltily, such as when he encourages Cassio to speak with Desdemona and then mutters disapproval to Otello upon his arrival. He also questions Otello about his trust in Cassio and his history with Desdemona.1
• Fabricating Evidence: Iago claims to have heard Cassio talking in his sleep about an affair with Desdemona.1
• The Handkerchief: Iago steals a handkerchief that Otello had given to Desdemona. He later ensures Otello sees Cassio in possession of this item, which serves as the visual "proof" that convinces Otello of his wife's infidelity.12
• Exploiting Context: Iago encourages Cassio to discuss his mistress, Bianca, while Otello watches from a hiding place; Iago ensures the conversation is framed in a way that leads the eavesdropping Otello to believe they are mocking Desdemona.2

By these means, Iago successfully traps Otello in a cycle of suspicion and rage.12