To select a file, click it once with your left mouse button.
To select more than one file (3 ways to do it):
- Hold down on your keyboard and click to select each file you want.
- If the files are one after another, click to select one file, then hold down on your keyboard and click the last file in the list that you want.
- Hold down your left mouse button, and drag a square around the files you want (as in picture).
When you have the file(s) selected, click Attach and you're ready to send it.