Just type letters, numbers and punctuation into the top box and press the "Translate" button. The program will place the Morse code in the bottom box, inserting a "?" if the character cannot be translated. If you want to translate prosigns, enter them as "<CT>" for instance and tick the "Use prosigns" checkbox in the advanced controls. This is not a great tool for learning Morse code as looking at the dots and dashes does not help. Instead, try the Morse Trainer.
You can type Morse code into the top box using "." for a dot and "-" or "_" for a dash. Letters are separated by spaces and words by "/" or "|". When you hit the "Translate" button the program will translate it into plain text. If it cannot translate a letter it will place a "?" in the output.
The "play", "stop" buttons control the playback. You can choose to hear the sound, see a flashing light or both using the "Sound" and "Light" checkboxes (unfortunately, in older browsers the light option is not available). There are also advanced options to control the pitch and speed. The "Farnsworth speed" is useful when learning Morse code as it can be set lower than the other speed in order to stretch out the spaces between characters and words whilst keeping the Morse characters fast.