Move plain SubRip captions into a format that can carry fonts, colours and positioning.
Open a project in the editor and go to Captions. You can start from a video you are captioning, or from nothing at all if you only need the file converted.
Bring in the SRT file. The cues and their timings are read in as they are, so nothing is re-timed and nothing is re-transcribed.
Export as ASS. You can also burn the captions into the video instead if you would rather they could never go missing.
SubRip is text and timings, full stop. There is no way to say what a caption should look like, so every player renders it in whatever default it prefers, and the same file looks different in three different players.
Advanced SubStation Alpha carries a style block: font family and size, primary and outline colour, border and shadow, alignment, and margins. It is the format subtitle groups and karaoke tooling settled on precisely because appearance is part of the content.
Converting up from SubRip does not invent a design. It produces a valid ASS file with a default style, which is then yours to change, so the value is in what you can do afterwards rather than in the conversion itself.
Not on its own. The conversion gives you a file that is capable of styling, with a sensible default applied. Changing the font, colour and position is the step that changes the look.
Desktop players like VLC and MPV do. Browsers and most platform uploaders do not, so ASS is for local playback or for burning into the video rather than for a web page.
Advanced SubStation Alpha is the later version of SubStation Alpha and adds most of the styling people actually use. Files usually carry the .ass extension.
Free, in the browser, and the captions can be burned into the video in the same place.