Twirl down any layer in the Timeline, and the Transform controls are revealed. On a typical layer, transforms are spatial data related to Position and its cousins Anchor Point, Scale, Rotation, and, um, Opacity. Opacity isn't really spatial transform data, but apparently Adobe decided to sort of grandfather it in here as an essential layer property; and "Transforms" evidently has a snappier ring to it.
A property in After Effects is a data channel found in a twirled-down layer. Typically a property can be animated and has a stopwatch icon beside it which, when clicked, sets a keyframe at the current time.
That by itself is simple enough. But there are, in fact, many different ways to animate a property in After Effects. How many can you think of? As an example, if you wanted to move a layer 200 pixels along the X axis over 24 frames, after setting the first keyframe and moving the time indicator forward 24 frames, you could
And those are just the options to keyframe that one property. You could also create the animation without key-framing a new Position value, and transform the layer 200 pixels on the X axis over 24 frames by
Don't worry, you're not going to be tested on these. But you can understand that there are many approaches to a given problem in After Effects, and the more of them you know, the more prepared you'll be for whatever comes your way.
If that's not crazy enough, you could even
The Transform effect exists for one reason only: to allow you to change the order in which Transforms occur. Normally, they occur before all effects, but this plug-in lets them occur after an effect is applied as well, without the need to precompose.
The last two options, in particular, are clearly designed for other, more complicated situations. Parenting is useful to transform several layers in the same manner, while expressions link two animations together, or create one from scratch.
Note that there is even a variety of ways to enter values while animating. You can
When dragging text in the Timeline or Effect Controls, hold down Shift to increment values at ten times the normal amount, or hold down Ctrl+Alt (Cmd+Option) to increment at one tenth the normal amount. The "normal amount" is typically, but not always, 1 for any given property; it depends on the slider range, which you can edit by context-clicking on the value in Effect Controls and choosing Edit Value.
But you can also work directly with the values found in the Timeline, and you can do so by highlighting and entering values, or by dragging on them without highlighting.
Keyframes and The Graph Editor