I started with a company 2 months ago and only work part time. I was told by a "shift supervisor" that if I only work 6 hours I didn't have to take a lunch. In the handbook (which I never received) it says "One paid 15 min. break and one unpaid 30 min. break for each 6-hour period you work."
I work exactly 6 hours each night.

My question is, first do I need to take a 30 min. unpaid break.
second. They are taking 30 min. from my paycheck each day for a break I didn't take. Can they do that?

MD has no laws that require rest or meal breaks be provided to employees 18 years of age and older; it's entirely a matter of company policy.

If you work through a break the company offers, you must be paid for it however. I suggest you discuss the work time you have not been paid for with your supervisor immediately. If that does not result in your being paid for that time, then you may contact your State's Department of Labor and file a complaint.

You'd better clarify with someone whether you are required to take a break or not.

If your employer says take one, you take one, regardless of whether it's required by law or not.

I was told at the beginning of the job that because I only work exactly 6 hours I didn't need to take one. I was told this by a shift supervisor. I read that if someone from management tells you something, that it is binding regardless of what the handbook says. Is that true?

No, it isn't, if you're saying legally binding. Neither your supervisor's word or the company handbook is automatically binding. And if the company is auto-deducting a lunch break, it seems to imply that your shift supervisor may have been wrong. That's why I'm recommending you check it out.