Follow the instructions there. Just root it and install a custom rom on it and set up a profile on cpu tuner and you should be good. Also get rid of any task killers those just suck your battery dry.
Its all good I didn't know that long ago either. The Rom is just the operating system on your phone. So right now you have a stock rom which is the OS your phone came with.
I know rooting for your first can be scary but if you follow the instructions then you will good.
I'm still learning myself so don't be scared to ask any question its better here then on XDA cuz they kinda expect to know everything.
Sorry I meant to say overclocked. So it has to do with the processor speed of the phone. The G2 stock is underclocked at 800mhz to save battery life that's why is has the best battery life out of other phones. I have my G2 overclocked to 1.8ghz which is faster then netbooks and computers with basic processors.
Any phone can be overclocked with something called a kernel which is a file that you put on your sd card that is flashed. Most custom roms already include a kernel that overclocks the processor on the phone.