LaTeX supports full document structure that includes chapters, sections and sub-sections of various depth.
\documentclass[11pt]{book}
\begin{document}
\part{First part}
\chapter{First chapter}
\chapter{Second chapter}
...
\chapter{Last chapter}
\part{Second part}
\chapter{First chapter}
\chapter{Second chapter}
...
\chapter{Last chapter}
\part{Last part}
\chapter{First chapter}
\chapter{Second chapter}
...
\chapter{Last chapter}
...
\end{document}
In Texifier, the full document structure is displayed in the Sidebar, providing an easy & quick way to navigate the entire document which may be spread over multiple files.