Like USB 3.0, USB 3.1 uses one legacy USB 2.0 differential pair, and two SuperSpeed differential pairs (for a total of 6 pins), plus pins for power and ground. Wikipedia has the pinout details.
USB C for USB 3.0/3.1 was made to work no matter which way you plug it in, so it uses roughly half the available pins, plus two pins to select which ones. Wikipedia as the USB 3.0/3.1/3.2 mode assignments, as well as the pinout.
From that, it should become clear which pins are connected to which, which play a special role, and why not all USB C pins are used.
The difference in speed between USB 3.1 and USB 3.0 is because USB 3.1 allows an additional encoding scheme over the same two SuperSpeed pairs, which increases the signal rate. Again Wikipedia has details.
And you didn't ask, but USB 3.2 can also use all four differential SuperSpeed pairs of USB C connectors over an USB C cable, which is why it can achieve greater throughput using such a cable. Again Wikipedia has details.