An interview for a job gives the employer the opportunity to find out more about you and to see if they think you have the skills and personality to fit into their business. But an interview should also be an opportunity for you to find out if the job is right for you.
Often the advert for a job posting only has very limited details and you will usually have a number of questions which you need to know the answer to before you can accept a position, should it be offered to you.
Although an interview is predominantly for the employer to find out about you and your skills/experience etc it is also an opportunity for you to find out about the job role and the company to see if you think it is the right job for you and you should not feel bad about asking a few questions. This also shows that you are confident and that you are making sure that you are suited to the job without just jumping into it.
It is always a good idea to ask a little bit of background about the company if this has not already been covered in the interview as this shows you are taking an interest in who you may be working for if things go well.
It is best to wait until the end of an interview to ask questions as you may find that your question is in fact answered.