I've downloaded behind bars and its not workin.

Edit: I'm using Technic Launcher

 It's a server only mod, it doesn't work on singleplayer. It says this on the download page, in the future please read the full description before downloading.

Please describe what you're trying to do, expected outcome, and what's happening.

This is assuming you're trying to run it on a personal server.

If you're trying it in singleplayer, as said by Malum, it won't work

 I am trying to run it on the public server 

Edit to title 

 THE  public server?  as in DMU public?  if so then theres your issue

( if not then i've wasted both of our time :P )

Dan I know what you mean. YOU can't use the behind bars mod on public. Only staff can, it is how we jail people when they are bad.

Ok this is the last time I am saying this. The Behind Bars mod download is so that SERVER OWNERS can put it in THEIR mod files and have it on THEIR server. Public already HAS the mod installed. If you put the mod inside YOUR mods folder in YOUR .minecraft then it does absolutely nothing. If you are trying to use the mod on the server to make your own jail then that isn't possible.

Give us an idea of exactly what you're trying to do with it

 Im trying to get it installed to the dalek mod on Technic Launcher.

Why do you need to install it though?

Unless you are running your own server you won't need the mod. The mod is installed on DMU to allow admins to jail users who are not following the rules.