From the Start screen, swipe left to display the applications list. Alternatively, select the right arrow ( located in the lower-right; may require scrolling to the bottom of the Start screen).
Select new ( located at the bottom).
From the 'To' field, enter a 10-digit mobile number. Alternately, enter a contact name. As the name is entered, a matching contact may appear and can be selected at any time. Alternately, select the plus symbol ( located in the upper-right), select a contact then select the appropriate mobile number (if applicable). Repeat this step as necessary to add additional recipients.
From the 'type a text message' field, enter a message.
Select send (located at the bottom; to the left of 'attach').