how can i know that what was the event for that they have sing that special song?

Question

for example rain of the samael band or bomb of the system of a down or any song that has a critical lyrics.

Answer 1

Try looking up the song on Wikipedia (http://en.wikipedia.org/wiki/Main_Page), alot of times they have entries on the stories behind songs.
Other good websites for insight into certain songs are Songfacts (http://www.songfacts.com/) and Allmusic (http://www.allmusic.com/)