Here is my 2 cents.
First, you will read enough articles to understand the current status of the
field or topics being reviewed.
In general, you will introduce the field of research, introduce the major
questions being pursued by various investigators, describe what have been
answered, what are being pursued at the moment, as well as the significance
and impact of these advancements, and finally, what are the unanswered but
significant questions as future directions.
Your ultimate goal is to let the readers know what's going on in the field.
The outcome is that they can cite your review when making some statements
without reading all original articles.