When you receive a text message with the Messaging app, you'll see in the status bar.
Read and reply to a message
Swipe the status bar down and touch .
To respond to the message, enter your response in the text box and touch .
Tips
You can save photos from messages. Touch & hold the attachment.
If you do not want multi-recipient SMS messages converted to MMS and want replies sent in separate conversations (threads) to you only, you can turn off group messaging.
Send new message
Touch > Messaging.
Touch .
Enter the recipient and your message. To send your message to a group, enter multiple recipients.