Just type letters, numbers and punctuation into the top box and the Morse code will appear in the bottom box with a "#" if the character cannot be translated. This is not a great tool for learning Morse code as looking at the dots and dashes does not help. Instead, try one of the training tools.
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 "/". The text translation will appear in the bottom box. If a letter cannot be translated a "#" will appear in the output.
The "Play", "Pause", "Stop" and "Repeat" buttons control the playback. You can choose between hearing the sound, seeing a flashing light, or having your phone vibrate using the "Sound", "Light" and "Vibrate" checkboxes. The "Configure" button reveals advanced options to control the frequency and speed and switch between telegraph and radio sound styles. The flashing light and download buttons do not currently work when in "Telegraph" mode.