I need help downloading tekkit

[brycegarner684]

Hello, I'm a bit of a computer dummy, so I don't know where to find information on this. I have a macbook I bought about 5 years ago, and it's upgraded as far as it will go at 10.5.8... anyways, I really want to be able to play tekkit with the boy I babysit, but when I try to open the .jar it just says it can't be launched... what do i need to do??? please help

[brycegarner684]

if no one can help me, can someone tell me at least where to look for information? I'm so lost on these sites... it's an OSX 10.5.8 macbook and the .jar file just says it can't be opened when i click on it. PLEASE help