How can I upload multiple files at a time?

It is possible to upload multiple files at once.  First, go to your Update Index and go to the File Management section as described here.  At the top of the page, you will see an entry box with a Browse button, allowing you to select a file for upload.

To add more boxes, click the "Add New Item" link immediately below this box.  Clicking this link will cause a new Browse box to appear.  You can add as many boxes as you like.  Each box can be used to select one file for upload.

Once you have selected all the files you'd like to upload using each of your Browse boxes, you should click the "Upload File(s)" button.  Clicking this button will cause all the selected files to be uploaded to your site.