it reallyreally simple and easy to use
download it here ->
http://www.videolan.org/vlc/
and then put the video file (usually .avi) and the softsub file (usually .srt) into the same folder
also make sure they have the same name
ex:
name.avi
name.srt
then open vlc player, and go to:
file -> open file
your video file location shouold go where it says "open:"
and then check the 'use a subtitle file' box
and put the softsubs where it says "file:"
and then click ok
and you're done =D
good luck!~