Describing your data with rich metadata and READMEs will help you and also other researchers to understand the meaning of your data, including what you did and why, and how to interpret your data. It is especially useful when you need to come back to your research data after a period of time, or when sharing your data while publishing your research.
Metadata is "data that provides information about other data" (Merriam-Webster); it tells information about data, which is essential for research data access and re-use. Depending on academic subjects, there can be disciplinary metadata standards that apply to specific disciplines, or general metadata standards that apply to all disciplines.
ReadMe files can be used to describe your project and your data. When depositing data into repositories, including a ReadMe file can help explain the files you've deposited. When you're keeping ReadMe files for your own records, it's good to have a top-folder ReadMe that explains all the subfolders and files that are part of the project as well as having them for lower-level files.
How to write a README file: