I plan to move to Sydney and seek a job. Currently, I generally use motorcycle to go around city. I am thinking about buying a motorcycle as soon as I reach there. But I have no idea about the viewpoint of people and the convenience of using a motorcycle in Sydney. Is motor riding popular in there? What is the process to buy and use a motor in Australia?
If you'll be coming in on a permanent visa, you have three months to convert your foreign license to an Australian license. The good news is that this is a fairly straightforward process; you should be able to walk into the nearest DMV office and walk out an hour or so later with an Australian license. And as long as you're over 25 years old you shouldn't have any trouble getting an open/unrestricted license.
The bad news is that if you've held your local motorcycle license for less than 3 years and are under 25 you'll get stuck with a 'Provisional' license instead of an unrestricted one. If you end up with a provisional license there will be a number of restrictions both in terms of what kind of motorcycles you can ride (i.e. only ones that are "approved for novice riders") and how you can operate them (i.e. not exceeding 90km/h even if the posted limit is higher, etc.). You'll also get hit with very strict rules with respect to demerit points, blood-alcohol limits, and so on. In short, you really don't want a provisional license.
More details here: http://www.rms.nsw.gov.au/roads/licence/moving-to-nsw.html
Is motor riding popular?
Can't say for sure.
However motorcycling has a bit of an image problem in Australia, unfortunately. There's a near-constant stream of articles concerning "outlaw bikies" and the heroic efforts of law enforcement and politicians to bring them under control. Some states have fairly draconian laws on the books that make it an offence to even be associated with any group that's deemed an "outlaw motorcycle club" by the political powers-that-be, even if no actual crimes have been committed by the accused.
That said, there are still plenty of motorcycle riders around. And with the traffic situation in Sydney, a motorcycle is certainly a more sensible option than putting another car on the road. A push-bike or using public transport would be even better.
What is the process to buy and use a motor in Australia?
Fairly comparable to the process in most other locales, probably. First, see the bit about getting an Australian motorcycle license.
Once you've got that down, you can purchase your desired bike from either a dealer or a private seller. If buying a used vehicle, it will/should already be registered, so you shouldn't need to worry about any extra costs until the existing rego expires, at which point you'll be on the hook for registration fees and also a CTP (Compulsory Third Party) insurance premium (covers you for liability should you kill/injure someone in a crash). With new vehicles, you may need to pay this outright on top of the purchase price (and if you're buying from a dealer, they'll walk you through the process).
The simplest option is to look for dealer vehicles advertised with a "Drive-away" price. That means that the listed price includes the cost of the vehicle, registration, CTP, and any other required fees/charges so that you can just pay your cash, fill out the paperwork, and ride home on your new motorcycle.
You may also want to look at augmenting the mandatory CTP insurance with a private comprehensive insurance policy (to cover things like damage to your vehicle regardless of who's at fault), but that's optional.