I personally prefer World of Logs also, but WWS specifically refers to wowwebstats.com, which performs basically the same function.
If you don't use an addon like Loggerhead, combat logging can be started at any time by typing /combatlog into the chat window - it will then output a file to your \World of Warcraft\Logs folder. From there you upload using the WWS or WoL client and it'll display all stats from when the combat log was started until when it ended.
One thing that may be worth bearing in mind - sometimes Vista doesn't seem to like you writing to the WoW directory unless you run it as an administrator, so check it's actually outputting a file if you're running Vista Home Premium or something