Introductory Structure of a Report Reviewing Established Knowledge
A document that collects and reviews knowledge already in existence is usually called a literature review.

It might be done according to a structured protocol, in which case, it is also called a systematic review.

And a systematic review that statistically analyses the data from existing primary research is also called a meta-analysis.

There are some excellent guides on how to write literature reviews, and Doing a Systematic Review: A Student's Guide  - Angela Boland et al is easy to read; it is primarily aimed at Masters students, but I think it's a good beginners' guide for most people who have to write a review, and don't yet have the experience.

Your introduction will typically identify what you are reviewing, what the context is, and possibly why this review is timely. It might identify how you selected your sources, and what the inclusion and exclusion criteria were (if this is so short that it does not merit a methodology section), and how many documents are included.

Many fields have journals dedicated to reviews: it would be worth reading a few reviews in your field, to get a feel for the structure. Your target journal's "guide for authors" may offer specific guidance: if it does, follow it!