When reading APL for the first time, how does one determine what the characters mean? E.g, the first example is (+⌿÷≢) x

I can look up the '+' '⌿' '÷' characters at https://en.wikipedia.org/wiki/APL_syntax_and_symbols but I can't find the "≢)" characters which appear to be the '≢ ' and ')' characters when I copy and paste. However, I see it as '≡' '/)' when rendered. Is that broken Unicode rendering of the slash? I'm guessing this function means something like (divide (reduce sum array) (count array)) but I can't search for that triple equal sign on the Wikipedia page.