After creating an empty stream you will be asked if you want to upload the files into the stream. If you want to do this later you can right-click on an empty stream and select 'Import Files'.
This will launch the Import Files dialog where you can select the local folder containing the files you want to upload. After this folder has been selected a list of all the files which will be uploaded is shown.
You can uncheck any files you do not want to upload.