Okay, let me help you understand the reasoning behind NM's questions with a little in-depth answer, dounuts.
Now we know you are flying Economy. You should be aware that Oneworld carriers FF programs credit economy flights at different levels - most will give 100% for all fare types on their own flights (planes) but a lesser rate (50%, some even 25% or nothing) for flights on partner carriers. So it's important to know what is your Itinerary looks like - to allow us to work out which program may give you the greatest opportunity for the most FF points and status. When you've got a fair idea of what it will be then give us a listing like:
QF SYD/HKG
CX HKG/LHR etc
You should also tell us what the fare basis of the ticket is - your TRavel Agent will be able to tell you. If you're on a Oneworld Explorer fare, then it will be a series of numbers and letters like YLEE1YR (I just picked them out of the blue, everybody).
So you're not going to take the flights at the end of the ticket (USA back to Aust); rather you'll have purchased another ticket USA to UK. Include those flights as well as part of the Itinerary for our calculations.
Does that mean that you are going to remain in UK and then use that as a base to then travel to Urope/North Africa/USA??
Now to the comment on status. Status is about the volume of travel you are taking in a membership year (from when you join). This is separate to the number of FF points your earn on those flights.
You earn status with the FF program by taking flights (but for some programs, not all flights will earn you status, just like the points differential above). The more flights that earn you status, the more benefits that the FF program will offer (like being able to check in at Business Class or special check-in desks, more weight for your baggage or pieces [for USA based flights]).
So, for example, in the Qantas FF program there are 4 levels of normal membership: Bronze, Silver, Gold and Platinum. Each flight is assigned a number of status "credits" , usually based on distance (the longer distance, the more status). So the more you fly and the longer the distance, the more status you earn.
Once you have earned a certain levels of status credits, you go up in level (for the remainder of your membership year). You will hold that level until you reach the next level (if you do within that same membership year). You then retain the level you achieved at the end of that membership year, for the entire next year; but the counter of status credits is reset.
I hope this has helped...