Some people, especially the non-native English speakers prefer to watch a movie or TV program with subtitles. Even the native English speakers need use subtitles if it is in a language other than English.
Mostly, people download movie from one source and the subs from another source. And that is where the problem arises.
The movie and the file may not be synchronized i.e. you may see the subs before or after the dialogues.
Before moving further, first you should know how to use subtitles files (.sub). My choice for a good subtitles experience is VLC Media player.
To sync the subtitle with the movie, play the movie along with the subtitle in VLC player. If you are seeing the subtitles first “press H” and if you hear the dialogue first, “press G“.
Pressing these shortcuts keys will delay or forward the subtitles by 50 ms. You can synchronize the subtitles with the movie this way.
Now, 50 milliseconds is not a lot of time and you may feel nothing has changed. If you want to move the subtitles ahead or back more quickly, hold the H or G key for some time.
This solution only work in the case when the delay between dialogue and subtitle is constant i.e. the sub intended for a movie with same frame rate. If you want complex editing, you need to use a proper subtitle editor.