To show subtitles on top of your movie you have two choices: 1. Use a media player that supports subtitles, or 2. install a subtitle software.
1. The quick and easy solution is to download the media player: VLC Player.
2. If you want to continue using your current media player, we suggest that you download and install DirectVobSub - it will also display special characters (including arabic) if you have trouble with those. It's a program that runs in the background and becomes active when you play a film with a subtitle.
In order to display subtitles make sure the subtitle file has exactly the same name as your movie (keep the filename extension (e.g. .SUB or .SRT)) and put it in the same directory as your movie.
Now when you start the video, the subtitles will automatically appear.
On MacOS, you can use Perian to do the same thing.