An important factor to remember about an interview is that it is a two-way street.
Certainly the hiring manager wants to ascertain if you are the right person for the position, based on countless factors such as knowledge, experience, team spirit, motivation, enthusiasm, education, employment history, and whether or not you will fit into the company culture, to name a few.
But you too are trying to see if this is the right spot for you. Yes, it may be that you need a job. It may also be that you have a pretty good job right now, and are comparing A to B. It is up to you to determine if this is the right place for you over the next few, or maybe many, years.
How do you determine this? You will learn some facts about the job from the hiring manager, and get a feel from the interview about whether or not you would wish to work with this person. You will presumably have read up on the company and know quite a bit about what they do, their products or services, their global locations if applicable, their performance on the stock market if they are public, and so on. The manager will assume that you know all this so asking about this would infer that you have not done your homework.
What then should you inquire about? Some suggestions:
a) If the interviewer is not the hiring manager to whom you would report, find out who that person is.
b) What is the size of the team you are joining?
c) Would you have any direct and/or indirect reports?
d) What essential experience / skills / education would an ideal candidate possess? Do you envisage me as having these?
e) What must you accomplish in the first year in order for the company to say that you have been successful?
f) What are the five year long range plans for this department/division?
g) What are the greatest challenges right now and where is the most input required asap? Do you see me as being able to help in this regard?
h) What is it about the company that the hiring manager has enjoyed most?
i) Is there opportunity for continuing training and further education?
j) If you are very interested in the position, and recognize that you can do the job, ask what the next steps are going forward.