To send a text message

On the Messaging screen, tap the New message icon in the upper right corner of the screen.
Enter a mobile phone number or email address in the To field.

As you enter the information, matching contacts appear. You can tap a suggested recipient or continue entering the phone number or email.

NOTE
Instead of a phone number or email address, you can enter a name. As you enter characters, matching Contact entries are displayed for you to select.
Tap the Message field to start entering your message.

A character counter is displayed to the right of the message field to let you know how many more characters you can type and also the number of pages in the message.
1. To field
  
  Tap here to enter the recipient(s).
2. Message field
  
  Tap here to enter your message.
3. Attachment icon
  
  Tap here to add an attachment to your message.
4. Character counter
  
  Displays the amount of remaining characters and the number of pages.
5. Contacts icon
  
  Tap here to enter the recipient(s) by searching through your stored Contact information.
If you tap the Back Key while composing a message, it’s saved as a draft in your Messaging application. Tap the message to resume composing it.
Tap Send to send the message.

Your message is displayed and responses appear in the same window, creating a message thread with that contact.