Once you have taken a photo or video, and applied your filters and text just hit the 'next' button. You will be taken to a screen with your followers. To send your message to specific people just select who you want to send to, and press 'send as a direct message' at the bottom of the screen.
You also have the option of sending the message as a broadcast to all your followers at once. To do this avoid selecting specific people and instead just press 'send as broadcast' at the bottom.
The next screen will allow you to set a view price - just adjust the wheel to the desired amount