Morse Code is just a simple substitution code, like all the others!
(table from Scouting for Boys)
Morse Code is sometimes written with a slash (/) between letters, to stop you from getting the letters confused. A double slash (//) means a break between words.
SOS = .../---/...
..//-./././-..//.-//--/.-/.--.//---/..-.//-/...././/.-/.-././.-//../--/--/./-../../.-/-/./.-../-.--//