It uses associative arrays, to understand how associative arrays work in awk, see this post
Unable to understand associative nature of awk arrays
About running this awk script, you have to use it in the same way as he coded, its as per your requirements, if you don't know how to run it at command line, then put it in some shell-script and run that file. Something like this:
Code:
#! /bin/ksh
awk '{ arr[length($1)]++; arr[length($2)]++; }
END {print "8 - 9 bytes", arr[8]+arr[9], " 10 bytes ", arr[10] } ' file
