Open the Times Table App project. Use currentProject to create a project object from the currently loaded project.

matlab.project.example.timesTable
proj = currentProject;

Create a new parent folder in the project folder.

newFolderPath = fullfile(proj.RootFolder, "newFolder");
mkdir(newFolderPath);

Create a new subfolder in the parent folder.

newSubFolderPath = fullfile(newFolderPath, "newSubFolder");
mkdir(newSubFolderPath);

Create a new file in the subfolder.

filepath = fullfile(newSubFolderPath, "newVariables.mat");
save(filepath)

Add the parent folder and its subfolders and files to the project. Check to make sure the file in the subfolder was correctly added.

projectFile = addFolderIncludingChildFiles(proj, newFolderPath);
findFile(proj,"newFolder/newSubFolder/newVariables.mat")

ans = 

  ProjectFile with properties:

               Path: "C:\myProjects\examples\TimesTableApp\newFolder\newSubFolder\newVariables.mat"
             Labels: [1×1 matlab.project.Label]
           Revision: ""
    SourceControlStatus: Added