I'm sure someone else who's done the entire process will post with more detailed info, but from what I can gather...
- you are expected to show up with your 70lb dog and an airline-approved travel kennel/carrier that will fit said dog (which will likely be huge, my lean/lanky 60lb dog will be in a size XXL due to the required head/tail/side room)
- you will show up several hours before the flight to check in with your animal (most airlines I've talked to have said 4, but check with whomever you book with), they'll likely check all your paperwork, make sure the kennel meets requirements, etc
- your dog will then hang out in the kennel until the time of the flight, when (I'm assuming) s/he will be sent out on a cart to the plane and loaded up
Then, post-flight, you'll head wherever they tell you to pick up the dog once s/he checks out on the landing side. Other posters have said this can take 1-4 hours, depending on the airline, how busy they are, etc.
The kennel doesn't need to roll, but the airlines do have specific requirements for how much extra space the animal has, that the door must be made of metal, there must be ventilation on at least 3 sides, etc. You'll want to check with your airline about their specific requirements. The airline may sell kennels themselves, but it's probably cheaper/easier to get one at Petsmart or something. (I took my dog there for a test run to try out various kennel sizes, actually, which was helpful since he really didn't want to get in the one I thought would fit him but was much happier one size up.)
Hope that helps!