Alt-click a stopwatch. Type some code. Done — you're writing expressions.
No setup, no IDE, no terminal. The feedback is instant and visual, which makes this the best possible way to start learning code as an animator.
The four you'll use everywhere
wiggle — shake a layer organically
wiggle(3, 20) // 3x per second, 20px max offset
loopOut — loop your keyframes forever
loopOut("cycle") // repeats forward
loopOut("pingpong") // reverses each loop
time — drive anything with the clock
time * 90 // slow spin. crank it up for faster
value — offset whatever's already keyframed
value + [0, -50] // push the existing position up by 50px
Linking properties
Drag the pickWhip from one property to another and AE writes the expression for you. Useful for tying a layer's opacity to a slider, or locking scale to a null.
thisComp.layer("Control").effect("Opacity")("Slider")
You don't need to write that by hand — just read it after the pickWhip generates it, and it'll start making sense.
Just start
Take any animation you've already built. Add one expression. Break it. Fix it. That's the whole method.