If you are playing retail only. Just download Deadly Boss Mods main package and DBM Dungeons (Dungeon mods recommended for retail)
If you are playing Cataclysm. Download Deadly Boss Mods main package and Cataclysm raid modules and DBM Dungeons (if you also want dungeon mod).
If you are playing Wrath Classic. Download Deadly Boss Mods ain package and Wrath raid modules and DBM Dungeons (if you also want dungeon mod).
If you are playing Vanilla Classic (including Season of Discovery). Download Deadly Boss Mods main package and BC/Vanilla raid modules and DBM Dungeons (if you also want dungeon mod).
Optionally, you can also add older content modules to classic as well, for example on cataclysm classic you can add wrath, TBC, or vanilla raid modules if running older content.