I assume your company had you sign a confidentiality agreement so that you wouldn't release trade secrets. You can still state why you were let go, what your job duties were, etc., but you have to be general when you say it. If you were let go due to policy violations, state that but don't give specifics that would allude to a practice. Or, if talking about your job duties, use general terms used in your industry.
Don't use that confidentiality agreement to fall back on so you don't have to answer any questions. Do you have a copy of it? If so, you may want to have it handy so you know what you can and can't say.