The Python Tutorial - 4. More Control Flow Tools, Guido van Rossum and the Python Development Team, 2024 - Provides the official and foundational explanation of Python's if, for, and while statements, which form the basis for nested structures.
Introduction to Computer Science and Programming in Python (MIT 6.0001SC), Ana Bell, Eric Grimson, and John Guttag, 2016 (MIT OpenCourseWare) - Provides structured lecture notes and problem sets from a highly respected introductory programming course, covering control flow and nested structures.