To send a text message, open up a conversation with a pal and tap on the keyboard icon to go on "text" mode.
You will find a textbox below. Tap on it to begin typing your message.
When you're satisfied with your message, tap on the "paper plane" icon on the right to send it.
To send emoticons, simply tap on the "smiley" icon, press on the emoticon you want. It will now be in your textbox.
If you're done, press the "paper plane" icon to send it off.