If you have no idea what you are doing, there are additional support centres in Australia. In WA they are run by the Small Business Centre company, and they usually have an outlet in each region. They basically know everything about starting a business, and offer advice. If you're not sure, ask them, or check their website. Some also run seminars - some are about serious things, some are about marketing on Facebook - but it's all helpful.
This does seem a little complicated - why doesn't nobody pay tax except for the final supplier? Doesn't the credit system add more complexity?
Well, it does, but not much. Suppliers report how much GST credits they are applying for, and how much GST that they collected, and pay the difference. Lack of collection up until the last retailer would most likely have a lot of fraud.
The GST credits work like this.
So, along this, there is $20 + $30 + $40 = $90 of tax. Does this go to the ATO? No, it doesn't.
So, in the end, $20 + $10 + $10 = $40 of tax is given to the ATO, which is the same as the tax paid to Supplier C by the consumer.
The good thing about GST is that the economic burden of the tax isn't borne by you - it's borne by the consumer. This works because as a business, you can get 'GST credits' for materials that you buy for making a new product, or (I believe) doing a service. Consumers, not being registered for GST, cannot claim these GST credits.
GST is optional if you gross under $75,000. If you decide to register for GST (for example, if suppliers request it - I know that Synnex, an IT distributor, do), the ATO gives you an extra benefit of letting you process your GST yearly, at tax time, rather than 3-monthly. I believe this sticks until you gross $20 million - then you have to go onto the 3-month "Business Activity Statements" method.
Once you have signed up and can use your AUSKey, you just "Add a Tax Type" in the business interface, under your ABN. This signs your ABN up for GST.
The AUSKey is used through a browser plugin. The browser plugin is, much unfortunately, Java. If you use Linux like me, give up here, find a copy of Windows, and install it in a VM. Don't bother using Chrome, just use Firefox. Save yourself the six hours of wrangling, it's not worth it.
Signing up for GST is easy - you need to register with the ATO. You can then get in with what's called an AUSKey - it's essentially a 'private key' for verifying yourself to the ATO.
Another thing to think about is the Goods & Services Tax - a tax that seems to be similar to VAT in the EU. It is a flat 10% charge. It either applies to things, or it does not. To the best of my knowledge, there are no other taxes for most items - it's that simple, easy to calculate 10%.
If you want to trade under your name (eg. Hawk Owl), then you're done here. If you want a business name (eg. Hawkowl Consulting), you need to register for an Australian Business Name. Once you have your ABN, you can apply for one from ASIC. Last time I checked, it costs $70 for a 3 years business name registration.
Last time I checked, that means that you're going to get charged less for tax if you're under about ~$300,000 income. Companies have a flat 30% tax, you do not, and it can be from 18% up. Check the Australian Tax Office for more details on this.
Your ABN is given to you - you are the business, and the business is you. You have unlimited liability for your business - which means you can mix personal and business assets (because they're your assets), and use personal funds to pay off business debts. All your profits go on your personal tax return, and you get charged tax at individual person rates.
Registering is easy, you go to ASIC's website, and sign up as a Sole Trader. You answer some questions, and then you get an Australian Business Number (ABN).
If you want to go into business for yourself, as something on the side, or just a venture where it's you alone, you can register as a Sole Trader with the Australian Securities and Investments Commission (the people that keep track of businesses, essentially).
Australia, from what I have read, is extremely business friendly compared to other countries. This stream is about what I've learned, starting up my own business.