Items on the BEGIN line happen before any lines are processed, so we set the standard FS (field separator) character to a :, then set a maxuid variable to 0. Then if the 3rd column (the uuid in /etc/passwd) is greater that maxuid set it to the new maxuid and set the maxname variable to the lines username which is column 1. Items on the END line happen after all lines are processed.

#!/usr/bin/awk -f
BEGIN { FS = ":"; maxuid = 0 }
$3 > maxuid { maxuid = $3; maxname = $1 }
END { print maxname ": " maxuid }
 

Since we added the awk shebang in the file, we can just run it with ./maxuid.awk /etc/passwd, if we hadn't added the shebang we could run it with awk like awk -f maxuid.awk /etc/passwd

Awk usually works on one line, but what if we have data like this:

Michael
Jackson
555-5551

Kevin
Jones
555-5552

To display

Michael 555-5551
Kevin 555-5552

ps -ef shows processes and how long they have been running in the hh:mm:ss format, lets print just the second column (the PID) and the running time but convert time into seconds

{ split($7, hms, ":")
    secs = (hms[1] * 3600) + (hms[2] * 60) + hms[3]
    printf "%6d %5d\n", $2, secs
}
 

Notice that count is not a built in function it's an array.

$1 != "USER" { count[$1]++; tot[$1] += $6 }
END {
    for (user in tot)
        printf "%8s: %4d %8d\n", user, count[user], tot[user]
}