Domino organizes work in Projects. A project usually includes two types of files - (1) user code and (2) input/output artifacts. Domino helps version and manage these files for you. Depending on project configuration (Domino File System vs Git service provider backing), there are differences in how the types of files are organized in projects, where they are stored, and how they are exposed in executions. For more information, see Git-based projects.
In some cases, small data files (for example, data mapping dictionaries) may also be managed as code or artifact project files, but this is only suitable if the files are small (less than 1 GiB) or if the overall size and number of such files is small (less than 50,000 files). For other data assets the recommendation is to use Domino Datasets.