You can interject your questions at any appropriate times during the interview. The interviewer may signal that the interview is ending by asking whether you have any additional questions If you do not have any concluding questions you may take this opportunity to summarize your value to the employer and repeat your sincere interest in the position based on the additional information you gained during the interview. Before you leave the interview be sure to find out the next step in the interview process. Offer a firm handshake at the beginning and the end of the interview. Do remember to smile and be friendly.
Employers appreciate enthusiasm.
Allow yourself time to think before you answer questions. It is appropriate to rephrase a question, or ask the interviewer to repeat a question that is unclear.