There is no 3D until you add a camera. Set perspective, push a panel toward you with translateZ, rotate it on all three axes, then flip a card. The Z-axis points out of the screen, at your face.
perspective lives on the parent and is how far your eye is from the screen — smaller = stronger, more dramatic 3D. translateZ moves the element along the Z-axis: positive brings it closer (looks bigger), negative pushes it away.
Tip: drop perspective to ~250px and watch the motion turn dramatic. Crank it to 1600px and it flattens out — that's a telephoto lens vs a wide angle.
rotateX tips it forward/back (nodding "yes"), rotateY turns it left/right (shaking "no"), rotateZ spins it flat like a clock hand. Combine them to aim the panel anywhere.
A flip is just rotateY(180deg) on a parent with transform-style: preserve-3d, two faces stacked with backface-visibility: hidden, and the back pre-rotated 180°. Click the card.
No backface-visibility? You'd see the back's text mirror through the front like a wet napkin. That one line is the whole trick.