Explanation
The key to this formula is the MATCH function, which is set up like this:
MATCH(MAX(LEN(name)),LEN(name),0))
In this snippet, MATCH is set up to perform an exact match by supplying zero for match type. For lookup value, we have this:
MAX(LEN(names))
Here, the LEN function returns an array of results (lengths), one for each name in the list:
{5;6;8;6;6;5;6;9;6;6}
The MAX function then returns the largest value, 9 in this case. For lookup array, LEN is again used to return an array of lengths. The after LEN and MAX run, we have:
MATCH(9,{5;6;8;6;6;5;6;9;6;6},0)
which returns the position of the max value, 8.
This goes into INDEX like this:
=INDEX(names,8)
INDEX duly returns the value in the 8th position of names, which is "Stephanie".
