How did iago makes othello suspicious

Iago plays on Othello's insecurities about Desdemona, and gets Othello to believe, through insinuation, that there is something going on between Desdemona and Cassio. Othello seizes on this, and Iago works at building up his suspicions. Soon, Othello begins to doubt his wife, as Iago lets his insinuations gain the force of an accusation against her. Othello begins to voice his insecurities when it comes to Desdemona, and himself as well. Desdemona enters, and they have a brief conversation; Othello admits that he is troubled, though he will not state the cause.