All messages with attachments that arrive in your mailbox are indicated by the  "Paperclip" icon.

When you open a message with attachments a list of the attached files is displayed above the body of the message.

To preview a file, tap on it.

You can save any images sent to you on your phone by opening the file and tapping  "Save".

You can send all of the remaining files as an attachment to a different message. To do this, open the file, tap  "Actions", and select "Send as attachment".

You can also open attached files in a different app. To do this, tap  "Actions" and select "Open in".