Google's big Gmail redesign earlier this year added a handful of new features, including Confidential Mode. The Android app hasn't gotten all the new Gmail tools, but Confidential Mode is rolling out today. You don't even need to update the app—just take a peek in the menu.
Confidential Mode sends emails that self-destruct after a given length of time. For other Gmail users, these emails appear in Gmail like other messages. For non-Google email accounts, the recipient will get a link to open the email in a secure web portal.
To send a confidential email in the app, start composing a new email like you always have. There's a new option in the overflow menu at the top called "Confidential mode." After selecting that, Gmail asks you to choose an expiration time and whether or not a passcode is required to open the message. You can always change your mind and remove or alter the confidential settings before sending the email.
If you were wondering what this looks like on the recipient's side, here you go.
Interestingly, getting a confidential email in the Android app prevents you from downloading image attachments. There's a banner at the bottom of the app that shows you when the message will expire as well.