When the Messages app is opened it is likely to be displaying one of its two main screens. These are the conversation list, which displays the latest message in all of your conversations or a screen showing all the messages in an individual conversation. The conversation list screen has a Messages heading and shows the most recent message in each of your conversations, either a messsage from you or your correspondent. The most recently active conversation is at the top of the list. If you want to read older messages in a conversation then you will need to double tap the conversation to show a screen which is headed by the name of your correspondent and lists messages in that conversation with the most recent message at the bottom of the screen.
When you open the Messages app it will display the screen you last used. It's easy to check by sliding a finger to explore near top left of the screen; the conversation list has an Edit button at top left and the screen displaying an individual conversation has a back button at top left. The back button speaks the number of unread messages before it speaks the words "back button". Don't worry if there are loads of unread messages. Only messages you read in the Messages app count as having been read so if you read them when they arrive as a notification that doesn't count as being read. If you find neither an Edit nor a back button you may have some incomplete work on screen. If you can't discover how to dismiss this, use the app switcher to close the Messages app and open it again. It should then be displaying the conversation list.
If you don't know how to close an app using the app switcher, here's how. If your device uses TouchID, double click the home button on iPhones or the top button on iPads. If your device uses FaceID slide a finger up from the bottom edge of the screen. You hear a sound on the first touch then two rising tones or vibrations as your finger slides upwards. Lift your finger when you hear the third tone or feel the second vibration. The app switcher is now started and you should hear "Messages, active". swipe up with one finger and you should hear "close Messages". Double tap to close the app. The app can also be closed with a single gesture, a three finger swipe up.
If the Messages app starts in the conversation list, you will be able to locate an Edit button at top left of the screen. You can swipe right to move past the Messages heading and reach the first item in the list of conversations. This will be the conversation with the most recent message. The message will be spoken in full by VoiceOver. If you don't want to hear that message you can pause VoiceOver speech with a two finger tap or simply swipe right to hear the most recent message in the next conversation without waiting for VoiceOver to complete speaking the first message. If you continue to swipe right through the list you will hear the most recent message in each conversation, which may be either from you or your correspondent. If you want to hear earlier messages in a conversation, activate the conversation by double tapping. VoiceOver's behaviour isn't consistent here so it's best to explore by sliding a finger above the bottom centre of the screen for the most recent message and lift your finger when it starts speaking. You can then swipe left back up the screen through earlier messages. You may sometimes need to scroll with a three finger swipe down. There will be a back button at top left of the screen to take you back to the conversation list. Alternatively you can go back with a two finger scrub gesture.
If the Messages app starts in an expanded conversation, then you can double tap the back button at top left to return to the conversation list if you wish. Alternatively, you can discover which conversation is on-screen by swiping right from the back button. You can then swipe right to move forward in time through the messages in the conversation or explore for the most recent message at the bottom of the screen and swipe left back through time.
If you want to reply to a message, locate it in the conversation list and then double tap to activate the conversation. Explore near the bottom of the screen for the text field in which you can write a reply. You will hear something like "message, iMessage, text field" or "message, text message, text field", depending on whether the recipient uses an Apple device or not. Double tap and you should hear something including "text field, is editing". You can now type, dictate or handwrite your message. Finally feel above the top right corner of the keyboard for the send, button and double tap. You should hear a whoosh to indicate that the message is sent. If you dictated the message, then you can proceed to the Send button with a swipe right. There is no cancel button to be used if you have second thoughts and decide not to send the message. If you wish to delete your reply, you can either shake the phone to undo typing or turn the rotor to Edit, swipe up to hear "select all" and then double tap to select all the text. Finally, use the delete key on the keyboard to delete the text.
All the messages in a conversation can be deleted when you are viewing the conversation list.
Locate the conversation you want to delete by finding its most recent message in the conversation list and then swipe up or down until you hear "delete" and then double tap. You will hear "Would you like to delete this conversation?"; you should now swipe right to find the Delete button and then double tap to confirm the deletion.
It is also possible to delete individual messages. Activate the conversation containing the message you want to delete and locate the message to be deleted and hear it begin to be spoken. Swipe up until you hear "more" and then double tap. You will hear "selected", followed by the message. Locate the toolbar at the bottom of the screen . It has two buttons; there is a delete button to the left and a forward button to the right. Locate the delete button and double tap. Finally confirm that you want to delete the message.
See Forwarding messages using the Messages app
Swiping up or down in the conversation list can also find the "hide alerts" feature. This will ensure that you aren't notified of messages from that person. This can sometimes be useful but many people turn this on unintentionally and then miss messages. If you use this accidentally, it is easy to revert. Find a message from the individual that you have accidentally hidden alerts from. VoiceOver will speak the word muted after their name. Swipe down until you hear "show alerts" and double tap.