Download the Telegram App on your smartphone. Android users can do so from Google Play Store while iPhone users can visit Apple App Store.
Now open the application and create your account.
Go to the profile of the user you want to contact then tap on the icon with three dots ‘…’
Now, select ‘Start Secret Chat’.
Note: Telegram secret chats are device-specific. If you start a secret chat with a friend on one of your devices, this chat will only be available on that specific device.
Once you log out, you will lose all your secret chats. You can create as many different secret chats with the same contact you like.