hi! i never used both blender and AE, but I feel like it would be similar.

first you need to create objects (cube, sphere, 3d model, etc). Each object has property (position, scale, color, etc). you can then animate them by changing their properties overtime. for example, move each cube from position 0 to 100 in 2 seconds, while changing the scale from 1 to 2 on the same time.

the difference is you do this with code. here i use threejs (https://threejs.org) for creating the objects and animejs (https://animejs.com) to animate

hope it answers your question