The separate subtitle-file should - of course - be loaded.
This can be done manually after having loaded the video-file (right-click followed by selection of "Load subtitles" ...etc.).
However, if subtitle-file is placed in the same folder as the movie-file and you give it the same name as the movie (except for the file-extension of course) this is not necessary as it will then load automatically.
Please let us know if you were successfull with the subtitles.