Subtitle are not working in vlc

Is it a single rectangle where the text should be or a series of letter sized rectangles?

If it is multiple rectangles then you probably are missing a font with the proper glyphs for the language you are trying to view. Look in Preferences ➔ Subtitles & OSD and report the Encoding and Font Selected.

For example if ဆဌဗရယမဝဪ appears as rectanlges and not the prettiest letterforms on the planet (Mayanmar) then you don't have Unicode support in your font. (I don't know Mayanmar so those are random glyphs, my apologies if they say something rude.)

The problem might be with the encoding of the subtitle file. Try opening the file and see if you can see the text in the text editor(you definitely should), if you don't, then get a different subtitle file.

If you are able to see, copy all text to clipboard, and save it in a new file as a plain text file with the extension ".srt" and replace the original file. Lock and load!

For VLC to pick up the subtitles automatically, make sure that the video file and the srt file have the same name.