1. A movie can have subtitles hardcoded into it. This means that the subtitles are permanent; they can't be turned off, they can't be edited or corrected.
2. A movie can be presented as a DVD. These have subtitles included in the additional tracks; you can turn these off if you like.
3. Subtitles can be provided as separate files which contain the text of the subtitles, as well as the time at which each line is to be displayed and the duration for which the line will stay on-screen. I like this approach best. It is very easy to open these files with Notepad and edit typos, grammatical errors, etc. Turning them off altogether is not a probem at all.
You can get these subtitle files from subtitle sites like
http://www.extratitles.to/,
http://subtitles.images.o2.cz/,
http://194.204.48.145/eng-0.php, etc. You can also get them by searching the ed2k network (use the same filename, specify a size less than 1 MB). Many release sites release the subtitles along with the movies. I wish FLM would do this more often.
There are a number of Software utilities that make the job of creating and editing subtitles very easy indeed. SubAdjust156, (DVD DIVx Tools) Subtitle_Studio.zip, and Subtitle Workshop v2.51 Multilanguage + Manual are my favourites, especially the last one.
Subtitle files for one release of a movie can be used with other releases as well, but they may need to be adjusted. eg. there are single file versions which need to be split for 2 cd versions of the same movie; a change in format between NTSC and PAL creates timing errors - the subtitles' timeline needs to be offset and stretched or shrunk to fit the movie. The utilities mentioned above do this with ease.
A number of media players support subtitle files. In addition to the ones mentioned in earlier posts, you have VLC and BSPlayer (my choice - very easy to use

). You can even use a subtitle file on your hard disk with movies on other media (eg. VCDs) - viola! you have subtitles for a movie that didn't have them earlier.
