There are many resources online to learn After Effects. I suggest having a good grasp of the 2D basics before moving to After Effects' 3D tools.
After Effects is a bit like Photoshop for video. It's a huge and powerful program, and will take some time to understand. A few basic concepts:
A project is where everything associated with your particular work is located. A project has one or more compositions
A composition is a combination of graphics. A simple project may only have one composition, a complex one may have hundreds.
AfterEffects layers are similar (but not identical) to Photoshop layers. They may contain still images, motion graphics, video footage, type, effects or 3d elements.
The timeline allows you to move through projects and compositions in time. Each layer has its own sequence of frames/
A frame is a single point on the timeline. When frames are played back rapidly, the illusion of motion is created. A typical frame represents 1/30 of a second.