Once you have opened the webpage in your browser, you may have to login to be able to send text messages to your phone. To do this take the 4 digit "Access Code" displayed in the iPhone application and enter it into the login page.
To disable this login feature simply switch the Security Code switch to the off position and you will never have to login again.
Once you reach the texting page you can type in the phone number(s) of the person(s) you wish to text and the message. Pressing "send" pushes the message to your phone where you are asked to confirm sending the message.