If you're just starting out, you don't need to run any scripts, battery tweaks, or do any overclocking. A ROM is just another OS for your phone. In order to overclock, do mods, or run scripts you need SuperUser, in Linux that means Administrator. In order to get SuperUser you need to root your phone. So if you want Cyanogenmod the process goes like this:

Root phone->Check if SuperUser works->Check if you have a Custom Recovery->Download a ROM->Go to Custom Recovery and Wipe Data and Cache then Flash It (Install It)->New OS on your phone.