Iago's motives are to seek revenge on Othello and Cassio both. Iago has these motives because the Moor has overlooked him for the lieutenant position and on Cassio because he was awarded the title. Iago also enjoys evil for evil's sake. He is one of the most villainous villains in all of Shakespeare.
The play is set in five acts with various scenes--typical of any Shakespearean play.
The play is set in Venice and Cypress because it must be an exotic setting because of the Moor and where he comes from. It must also be there because the Turks are a naval fleet and the backdrop to the play is the war the Venetians are waging with the Turks.