Hi Sandra, 

Welcome to Box Community and glad to help! 

To add new files into your folder, please follow these steps: 

1. In the All Files section, select the folder and click New + button in the upper-right corner.


2. Select File Upload or Folder Upload, depending on what you'd like to upload. 


3. Select the file(s) or folder you'd like to upload.


4. You can select multiple files for upload by holding the Command or Control key (Mac or Windows, respectively) while selecting files. However, you can only select one folder at a time for upload.


5. Click Open or Upload.

Hope it helps!