Prepare job summaries, if relevant. You can use the job description template you use for each position that you advertise by filling in the template with the information that is relevant to that position. However, if you do (or expect to do) a lot of hiring of a particular position, you might make a special template that includes a summary of that job. This will save you some time.
Think of this as describing the purpose of the position, and its role within your company or organization as a whole. A job summary will briefly acknowledge the fundamentals of the position, so leave space on your job description template to answer.