A sidebar layout places a narrow column beside the main content. It is like a book with a table of contents in the margin, so readers can jump to a section while keeping the page in view.
Documentation sites often use a sidebar to show sections and sub-sections. The large area beside it displays the chosen page.
On a phone, the side column may need to become a menu that opens when requested. Keep the main content wide enough to read and make the selected section easy to spot.