Hi Cheryl
Another Aussie here. I actually grew up on the Central Coast (where Gosford is) and lived in Gosford so I know where you are going.

You can drive there if you are hiring a car or catch a train and walk. The stadium is across the road from the Central Coast Leagues Club
www.cclc.com.au and is only a ten minute walk from the train station. If I were you, I'd actually catch a train, the ride is only about an hour (maybe an hour 15) from Central Station (Sydney city) and is a very easy journey. If you want/need any help with directions to Gosford send me an email and I'll help out any way I can.
I hope you have a great holiday.
Jayne