MasterH0rnet

Heyho, I'm fairly new to private Servers and Stopped my WoW carrier shortly after the release of TBC, so please forgive me if this question ist stupid, but I was wondering how its possible for me to join a Server that runs on version 1.5 while my client is 1.12. I would expect that I'm at least lacking some textures, sounds etc. of the newer version. How does this work and do I need to upgrade my client to enter Dire Maul? thank you for your time!