I'm not the type of guy who mod the game, but i would like to have the music in the game by the addon.
But i don't know how to add it.
can someone help a noob please.
thank you

You dont need to mod the game, you need to mod the music.
https://en.lfsmanual.net/wiki/Options#Audio

Quote :

In-game music:
LFS supports playlists and here you can see and change which playlist is being used at the moment. Using 'Skip' you can advance one song and using 'Select' you can directly choose a song.
Channels:
Using this button you will enter the interface for playlist creation and editing. Channel 1 is the standard for all setup screens and can not be deleted. You can add, rename and delete playlist on the left of the screen. On the right you can add tracks assign a song to each track and delete tracks. To ensure that a track will be played back you have to its priority with 3 being the highest priority, 1 the lowest priority and – the setting to prevent a track from being played. The higher the priority of a song the more likely it is that it is being played back. This means that if you have two song of the same priority you will hear both song equally often but if the one song has a priority of 3 and the other a priority of 1 you will hear the first song much more frequently.
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The music files of LFS are in OGG Vorbis format. You can convert your own music files using a freeware encoder available at www.vorbis.com or using Audacity or a similar audio editor. To play the songs back within LFS they have to be in the data\ogg directory.

Really less hassle to put up some music player in the background instead of using this obsolete, underdeveloped feature of LFS thought.