In Othello, how does Cassio exploit the three women in Act 3, Scene 1?

If your question refers only to Act 3, Scene 1 of Othello, Cassio doesn't "exploit" three women in the scene. He does wait outside Othello's residence hoping for a chance to speak to Desdemona. In that sense, he uses Emilia (Iago's wife and Desdemona's maid) to get to Desdemona, and he plans to "use" Desdemona to put in a good word for him with Othello so that he can get his position back. "Exploitation" is a rather strong word for Cassio's plan, but he is undeniably looking out for himself without considering how his talking to Desdemona secretly might hurt her relationship with her husband.

In other scenes, Cassio mentions his relationship with Bianca, and he certainly exploits her. In Act 4, Scene 1, Iago asks Cassio about his intentions regarding Bianca because she allegedly has been telling people that Cassio is going to marry her. Cassio's response to Iago is:

"I marry her! What? A customer! I prithee, bear some / charity to my wit; do not think it so unwholesome. Ha, / ha, ha!" (4.1.135-137).

It is obvious that he views Bianca as a passing fancy and as an inferior. This conversation, more than any other dialogue featuring Cassio, demonstrates that he is not wholly the thoughtful gentleman who he purports to be to Dedesdemona.

How does Cassio exploit three women in Act 3, Scene 4 of Othello?

In Act III.iv of Othello, Cassio uses Desdemona and exploits only Bianca.  He has no real relationship with Emelia.

Cassio cares more about his lost reputation than he does about the reputation of women.  To him, as it was for most men of the time, women are second-class citizens, far down on the social ladder.  Ironically, since Cassio has lost his reputation, he has joined the women in status: he's as far down the ladder as they are, maybe lower.  As a result, Cassio appeals to Desdemona to act as a go-between to help him regain favor in Othello's eyes.  Honestly, this is immature, if not pandering.  He uses, if not exploits, Desdemona's virtue for his own purposes:

I do bessech you / That by your virtuous means I may again / Exist, and be a member of his love / Whom I, with all the office of my heart, Entirely honor.

Cassio is not as naive as she; he should know that Desdemona's appeal might very well anger Othello and make him jealous.  He appeals to her anyway; he intentionally puts her reputation at stake to save his own.  Cassio resents his status as equal to women; therefore, he uses the best of the women to help him move toward again becoming superior to them.

As for Bianca, Cassio exploits her for pleasure.  She is his courtesean, and his speech toward her is rather sexist.  He calls her his sweetheart and acts impatiently toward her:

Go to, woman!  / Throw your vild guesses in the devil's teeth, / From whence you have them.  You are jealious now...

Cassio exhibits the classic male double standard: he may be jealous of Othello's reputation, but Bianca may not be jealous of another woman's.  Later, he uses understatement (litote) to placate her.  He says that he "doesn't not love her" as a clever way of keeping her around for his sexual purpose:

Not that I love you not.

He uses the handkerchief in the same way, as a means of keeping her.