1. Open Messaging
2. Touch the compose icon(should be placed on the lower left side of the screen)
3. Enter the contact you want to send a message to
4. Tap the Type message field and use the on-screen keypad to enter a message.
5. Press Send(that icon beside the type message field)
Source: user manual p. 108 which you can download for free on Samsung Galaxy Centura page here on TheInformr.