The SubRip file format may be the most basic of subtitle file formats but it is very useful. There's information on it on the Matroška website, but you can work out the format by looking at a .srt file in a text editor. Note that as SubRip was written by a European a comma "," is used rather than a fullstop "." for the decimal point separator.

An example:

1
00:00:38,879 --> 00:00:40,647
Once every 120 years...
2
00:00:42,315 --> 00:00:46,920
A "shinigami" appears
from the eastern seas.
3
00:00:47,854 --> 00:00:49,289
What is a "shinigami?