>>
>>Googling for 'file extension srt' gives the first link http://filext.com/detaillist.php?extdetail=SRT
>
>Thank you, Sergey. I guess there is some kind of a player that takes these files and shows them as subtitles. I need to find out more.

As my son explained to me, for Windows you'll need VobSub plugin. You can download it from http://www.free-codecs.com/download/VobSub.htm, for example. You have to put SRT file into the same directory as movie and give it the same name as movie.