So in that sense, if GNU/Linux is your main operating system and want to learn how to edit/create subtitles with ease, then I highly recommend this amazing little application called Gaupol. It's written in GTK+ toolkit thus aimed at the Gnome Desktop (obviously) but of course we can use it in KDE or other GNU/Linux desktops as well.
But remember, you however cannot load subtitles that are embedded into the video container it self. In that case you'll have to extract them from that multimedia container first.
*. Supports almost all the major subtitle formats such as - .ssa, .sub, .srt, .txt, etc. Again, if you have a DVD, then you'll have to extract the subtitle from the .vob format first.
*. Very easy to use but extremely powerful features (hard to believe actually.. I mean, after all it's a GTK+ app, they usually drift towards Gnome's version of simplicity... but have to say it.. well done -> to the developer).
*. Auto spell checking.
*. Change FPS (can be used to fix invalid subtitle display times... not always though).
*. Split subtitles.
*. Easily merge video subtitles (say that you have 2 subtitles for cd1 and cd2... but would like to merge it to a single file... not that easy since you have to manually edit the time delays, etc but possible).
*. Insert new subtitle to the current one.
*. Shift entire positions.
*. Unlimited undo capability.
*. Remove hearing impaired texts.
*. Save in different formats.
*. Search and replace specific words/texts.
*. You can even play the subtitle with the proper video file and make a live preview too!.
These just the main features of the amazing application called Gaupol to name. To be honest, this is one of the best video subtitle editors that I've come across, so far.
If you use Ubuntu 11.04 Natty Narwhal or 10.04/10.10, and want to learn how to install Gaupol, then use the below command in the Linux command line (Terminal).
sudo apt-get install gaupol