When uploading files to your My Documents area, only you can see and have access. You have the ability to share the documents within this area.
On how to upload documents to your Organisation space, see here.
Select the file you would like to upload and click the Open button
The file will then start to upload. The upload dialogue will appear at the bottom right of the screen to display the progression of the file being uploaded
The file will now appear in the My Documents area within Nucleus as shown in the below screenshot