How do you understand and analyze someone else's program code?

To understand and analyze someone else's code, I usually follow these steps:

1. General overview: Quickly review the project structure, main files, and folders to understand the scope and scale.
2. Read documentation: If there is a README, comments, or specifications, I study them for context.
3. Run and test: Try to run the code to see how it works, what input and output data it has.
4. Step-by-step analysis: Read the code by modules or functions, trying to understand the logic and purpose of each block.
5. Use debugger: If necessary, run the code in debug mode to trace the execution flow and variable values.
6. Notes and refactoring: Make notes, comment on unclear parts, sometimes rewrite sections for better understanding.

This approach helps to systematically and effectively understand even complex чужой код.