I am going to be installing a concrete driveway. I have tore out the excisting asphalt driveway and formed up for the concrete. How do I install the expansion joints? Do you pour the concrete in one pour and then use a saw and cut the concrete where the joints need to go in? How often do they need to be placed for a 17′ by 78′ driveway?

The expansion joints are formed either by you putting thin wooden slats in that leave slots, or, while you are smoothing the surface, you actually shape the slots with your trowel.
Usually the individual section can be about 4′ x 6′, and larger if you use heavy duty steel grids to strengthen the concrete.
With your measurements I would do one down the center, and the others at 6′ to 8′ intervals.
Since this also depends on the quality of the concrete you’ll use, you may want to double check that with your concrete supplier.
Depending on the size of the vehicles you’ll be running across that, I would think that you want at least a 6" thickness, and more if the underground isn’t very hard and stable. Use one to two inch gravel as a base.
I did that on a driveway 38 years ago and it is still perfect.