Explain the details regarding Iago's plot for Cassio's downfall. How does he convince Roderigo to become involved in it?

Iago convinces Roderigo to become involved in the plot by insinuating the man has a chance with Desdemona. He tells him that Desdemona has already strayed from her husband and is having an affair with Cassio. Iago adivises that Roderigo just might be able to get rid of Cassio by picking a fight and causing him to be demoted.