After entering your five digit code, there is a box to read some random numbers/letters located about mid-way on the page. This is a security measure to "prove you aren't a robot".
Sometimes it may be difficult to read these numbers/letters, however it's ok to take several attempts. New codes will be generated that might be easier to read.
After that you will see a button on the far right that reads, Transmit Return. Once you click this button, your return is sent.
