How and why do you 'manage data'?
Throughout your research project, you may be handling a lot of data: financial data, crime statistics, text corpora, biological data, etc. It is necessary that you understand how to stay organized and adhere to standards and best practices. Good data management leads to successful projects.
It will also be important for people outside of your project to be able to find and navigate your data in case you must provide further evidence in the form of raw data and if you decide to share the data as supplemental article material or archive it in a repository.
Furthermore, funders like the National Science Foundation (NSF) and the National Institutes of Health (NIH) require data management plans as part of grant applications. It is important for you to know what they expect, since part of your grant's chance of acceptance depends on a good data management plan.