Please describe a stack and the two operations it performs.

When an interviewer asks you to describe something, you should immediately identify the question as being technical. When responding to a technical question, you first define the term or concept and then describe how it is used in the work you are performing. If the interviewer asks you follow-up questions, they are expressing a strong interest in this topic and indicating that it is important to their operations. This signals you to expand on your answer and give them more details than you normally would.