Hi Robby, and welcome
It sounds like you're on the right track if you're working through projects in the book and have a decent grab-bag of parts.
specifically, which pins does the shield actually use for the motors, and how do I use the pins that it’s NOT using?
That motor shield uses digital pins D8 through D13 so on a Uno that still leaves a good number of IO options:D0 & D1
Normally used for serial IO and debugging, but when you don't use that you free these up for use. Also useful for serial comms over radio (bluetooth, Bees, etc)D2 - D7
General digital IO, D3, D5 & D6 are also capable of PWMAnalog 0-5
For analog inputs, and these are also addressable as digital D14 through D19 if you need extra general IO pins.
All I can suggest is keep pushing on with it, there's lots of fun and the glow of achievement ahead, and when you get stuck - shout out. There's lots of folks here to assist when you do.
All the best! Geoff