Timing is the whole code
Morse code has only one symbol, a tone, in two lengths. A dot (dit) is one unit, a dash (dah) three. The gap between parts of a letter is one unit, between letters three, between words seven. Speed is given in words per minute using the standard word PARIS (50 units), so at 20 WPM a dot is 60 ms. Everything else, including the dots and dashes on paper, is a transcription of that rhythm.
The design
Samuel Morse and Alfred Vail assigned the shortest codes to the most frequent English letters, which they estimated from the type cases in a print shop: E is a single dot, T a single dash, while Q and Y are long. That makes Morse a variable-length prefix-free code more than a century before Huffman formalised the idea. The international version (ITU) regularised Vail's American code in 1865 and added letters with diacritics for European languages.
Prosigns
Procedural signals are letters run together without the gap, written with a bar over them: SOS is not three letters but one nine-element sign, chosen in 1905 because it is unmistakable, not because it stands for anything. AR ends a message, SK ends a contact, BT separates paragraphs, and eight dots mean “error, ignore the last word”.
Still in use
Amateur radio (where it punches through noise no voice mode can), aviation navigation beacons that identify themselves in Morse, assistive communication for people who can only move one muscle (Google's Gboard has a Morse keyboard), and the odd Easter egg. The audio player here uses the Web Audio API, so it works offline once the page is loaded.
Questions
What is SOS in Morse code?
··· ––– ··· : three dots, three dashes, three dots, sent as one continuous sign. It became the international distress signal in 1908.
How are spaces between words written?
Conventionally with a slash ( / ) or with a wider gap. This translator accepts either when decoding and writes a slash when encoding.
Why are some letters not translated?
Only characters in the International Morse table are encoded; the tool lists the ones it skipped. Most Latin diacritics have codes; symbols like # or emoji do not.
What speed should I practise at?
Learn the rhythm at 15–20 WPM character speed with extra space between characters (Farnsworth method), rather than slow dots that you would later have to unlearn.