To understand the structure of systematic reviews, the most efficient way is to look at the systematic reviews that have been published. Here are a few databases that can help you find existing and ongoing systematic reviews (protocols).
A MOOC course "Introduction to Systematic Review and Meta-Analysis" provided by the Johns Hopkins University, is free for access at Coursera.
It is a good self-learning online open resource on the subject. The contents are made very easy to understand, delivered in short videos with transcripts.