Sharing files securely from within the iPhone app is super easy.
Launch the app from your home screen.
Enter your passcode (if you've configured one).
Choose the file that you want to share, and swipe right.
A menu appears. Choose the type of share that you want to create, either E-mail link (public), or E-mail secure link (secure).
Once you have entered the recipients' email addresses, tap Done.
Your file has now been shared.