The format is "Unix time" (seconds since Jan 1, 1970) with millisecond resolution.
You can use perl to make the time human readable.
perl -pe 's/\d+/localtime($&)/e' /var/log/squid/access.log
or use log parsers that will produce pretty reports from squid logs as web pages, like webalizer.
Also tell me how to run a file in LINUX
Which file do you mean?
Make the file executable