When you log in to your account, click on the "Submit Message" link at the top of the screen. You can publicly share the URL for this page wherever you're advertising your tip line. You'll notice some instructional text is only visible to you with suggestions for sharing your address.
You'll also see a message indicating if you've uploaded a PGP key. This will be visible to someone submitting a message, so if you'll receive sensitive information, it is advised to add your public PGP key in Settings.
When you share the address, someone sending a message will see slightly different text, with voice and tone directed at them.
If you haven't added a PGP key, you and any visitor will see a warning that messages will not be encrypted.