Most high-def TVs have USB ports which can read .avi files, the standard format of downloadable movies. If your file is not in the avi format (and your TV USB player cannot play the current format), convert it into .avi or any other supported format.
2. Downloading the Subtitle
The most popular format of subtitles is the .srt format. There are several websites that let you find your movie, the language and then download the subtitle. I prefer SubtitleSource.org. Simply Google for "download subtitles" and you'll find plenty of other sites to download subtitles from, if you are not satisfied with your current subtitle.
3. Renaming the files
This is the most important part. Without it, you will not be able to play subtitles along with your movie (at least not on your TV). But it's real easy. All you have to do is this : rename the movie file and the subtitle file so that both have the same file name (except for the file extension part). The file extension is the last part of the file name (.avi and .srt in this case).
When the video file and the corresponding file have the same file name, they are played together. Transfer them to a USB and plug it in to your TV.
Congratulations, you can now play movies with subtitles on your TV !
Note : More guides on playing subtitles are coming; they will be linked soon.