You can have an outline in an R script of the function and the section.
See on the right and at the bottom. Some keyboard shorcut can help you navigate quickly.
In an Rmd file, you will have the same with
- an overview of all titles in your doc on the right (a TOC)
- an overview of all titles all all chunks (using named chunk is better) at the bottom
There may be other feature but I kown and use these ones for now.