Previously when I wrote a guide on this same topic, I was mistaken. That's not the simplest way.. not even close.
Here's the real and bogus SIMPLEST way to find subtitles for your movies.
1) Install and launch Sublight. On first launch it will enter the settings wizard, be sure to follow it step by step as it is the gateway to immortality.
2) *Important* there's one more setting to be set before your power can be fully unleashed. Go to 'Settings' tab > 'Explorer Integration' > check 'Enable Batch subtitle download' and at the bottom of the screen, check the formats that your movies are using. If you're not sure, just check them all. Click 'Save and apply changes' at the top left of the screen. You may now close Sublight.
You only need to do the first two steps once. After that, all you have to do next time is just step 3..
3) Right click your movie and select 'Find subtitles'
4) Select the subtitle that matches your movie and click 'Download' to get the subtitle file downloaded beside your movie file.
PS: The subtitle you download may or may not be perfect for the movie, download the one that you feel most likely the correct subtitle (base on the number of CDs, movie title, number of downloads, ratings etc.)
Read here if you wish to learn more on 'Batch subtitle download'
There's a very useful feature that helps you to download subtitles for every single movie in your folder. To use it, first you need to register an account.
1) Click the green color menu button > 'Register new user'. Follow the steps to get yourself registered.
2) Right click the folder that contain your movies and select 'Batch subtitle download'.
3) In the next screen, enter your Username (used in the registration above) and click 'Run SublightCmd'.
4) Enter your password when prompted in the next screen. After that the program will run by itself and download all the subtitles in the folder. It will try to download the most appropriate subtitle for each of the movies but there's no guarantee as there are so many different versions out there.
It might take a while so go grab a coffee in the mean time :)
End note:
If you couldn't find your subtitle, you can always use my old guide (website method) to find it. As sublight is community driven, if you found a subtitle suitable for your movie, you may volunteer to upload it :) This will give you sublight points. Sublight points is used when you download subtitles, if you don't have enough points, you'll have to wait 10 seconds before the download begins. There are many ways to earn points, read the FAQ for more information.