Open several files at once
Click the Open button. This will cause the Open dialog to appear.
From the Open dialog, you can select more than one file with the Ctrl or Shift key.
If you hold down the Ctrl key while you select a file, that file will be added to the selection.
If you hold down the Shift key while you select a file, the selection of files will contain the first file, the last file, and all of the files in between.