Programs: DL girl's best friend, SC Lifetime(DL's not mine), ST E+, IC RA, SPG, AARP, CARP, Nexus/GE, APEC
At DFW, assuming you are flying in from Australia:
You have to enter into US through immigration, then you pick up your check luggage to go through US customs. After clearing custom you drop your bags off at onward connection. Then you enter into DFW terminal going through the TSA security check point. If you are fortunate your departing flight will be in the same terminal.
Best if you can go direct to YVR or via an Asia country which has transit area without all these hoops to jump through.
Some airlines can provide someone to assist a passenger, though a fee may be required. They could at least direct you to the right places, but probably not going through Immigartion, etc. Signs should be plain, and your other passengers will be going to the same place (follow the crowd).
Be sure to fill out your Customs form, given to you in the plane, before you get to Immigration. When you get to Immigration, you usually need to go to one of two lines: U.S. citizens/permanent residents, and all others. Immigration officer will process your entry (you'll need to have your photo and fingerprints taken if you're not a U.S. citizen), and will initial the Customs form. Then there should be just one direction to go to the baggage claim. Then you go through Customs (again, just follow the signs or ask). Going through Customs normally consists merely of handing over your form. You could be asked to step aside for secondary inspection (could just be at random, so don't worry). After that, you go to a transit desk to hand over the bags for any onward flight (if somehow you don't see it, just ask, and make sure you don't follow those exiting the airport). Then, you go through security and walk to the gate for your next flight. It's really not a difficult procedure. And there should always be people to ask if you feel confused.
Remember that if you bought any liquids or cremes, etc. (items not permitted on planes) in Duty Free, including on the plane, and they are in your carry-on bag, you should transfer those to your checked luggage before you hand the checked bags over at the transit desk, otherwise the Duty Free items could be confiscated when you go through security (happened to my wife at ATL).