I have built a car that will drive myself and just need to know where to connect the ultrasonic sensor and my LCD display to my motor sheild expansion that sits on my arduino uno. I want to connect these two because it senses distance and reads it simultaneously on my LCD display.
I imagine the ultrasonic sensor could go on any pins the shield doesn't use: check the documentation to see what's vacant. I've only ever used an SR04 though.
And I2C uses whatever pins are set aside for that purpose on your board; A4 and A5 on an Uno.