Run it, pick .srt subtitle file, then it will generate a Shotcut .mlt project file in the same folder.
Open the result.mlt in Shotcut as a new project, or import .mlt as a clip in the existing project.
If you use it on music lyrics .lrc or other subtitle files like .ass etc, use an online converter to convert it to .srt file.
The .srt must be pure text subtitle, without special formattings. Open your .srt subtitle in text editor and check for like <i> <b> </b> or any other fancy format, batch remove them before use this tool.
If you need to change font color or font size etc. use text editor search/batch replace in the result .mlt file.