There's a few things you need to sort to have before you can emark on your first commute to work.
The most obvious thing you'll need to commute by bicycle is, wait for it...... a bicycle!
The variety of TypesOfBikes available in Australia is huge, so huge they've got their own set of pages. I'll not go in to the variety here but you need something that's in good mechanical condition, reliable and comfortable. It needs to be good enough to do the job but not so good that it'll dissapear in to the van of professional bike thieves as soon as your back is turned.
Even if you're planning on cycling in daylight hours there will come a time when the sky goes dark and the rain comes down. A cyclists first defence is being seen and modern bicycle lights do an excellent job of helping that.
It's adviseable to have enough tools and knowledge to keep yourself going. The most common mechanical to befall a cyclist is the dreaded puncture. A spare tube, tools to get the wheel off your bike, a puncture kit, tire levers and a pump will get you out of trouble. For most people this is sufficient.
A helmet appears to be no necessity unless you are obliged to wear it. See the linked article. Under New Zealand law, and in some other jurisdictions (most Astralian states, many US municipalities) you are obligated to wear a helmet. Get one, get a good one, get one that fits. You'll be wearing it every time you ride your bike so spend the money and make sure it's comfortable, and fit it correctly.
Entirely a personal preference. Generally the further out you are from your destination, the more likely it is that you'll be wanting specific clothes for cycling. If you destination's less than 10kms away you can get there wearing normal clothes provided you don't ride too hard, most cyclists in Australia prefer to ride in clothes designed for the job. If there's one piece of advice I can give on this it's this, Wear Lycra.
You might be lucky, you might have an office that you can store your bike in, there might be room behind your desk. Your work may have dedicated bicycle parking. The fact is that you need somewhere to leave your bike and it has to have something suitable to LockYourBike to.