Layers are the essential building blocks of After Effects, without them, the program would be useless. They are simply containers that hold media, however there are a number of different types, each that perform slightly differently from one another.
An adjustment layer is nothing but a dummy layer which is invisible in the composition, this is useful when you want to give the effect to all the layers in your composition.
The solid color layer is simply a flat layer with the selected color of your choice, this is useful when you want to check keying result, for backgrounds and some other times.
Type layer: with this layer you can add titles in your composition, it deals with text.
Light layer gets applied to only 3d enabled layers,.,., it throws a light on your object or layer and you can choose how should that appear in settings,..,. you have various lights to experiment.
Camera layer: you can view your 3d layers from many angles and distance using the camera. If you create a camera layer and from view option, if you select your camera, you will be seeing your composition through that camera. Camera layer has almost many settings that make the view like real cameras which are used to record the footage.
Null object layer: null object is an invisible layer with all the properties of a layer which is visible, it can be a parent layer to any visible layer in the composition. Whatever you do with the null object, it will be applied to the layer which is linked.
Shape layer: with shape layers, you can draw shapes like rectangle, ellipse, etc and you can do lots more with its features.
Content-aware Fill Layer: lets you remove unwanted areas or objects in video footage, while automatically filling in the area of the removal. It analyzes frames over time to fill in missing pixels by pulling them from other frames in the footage.
Photoshop File and Cinema4D File You have the option of directly importing either .psd or C4D files, the benefit of this is that you can always go back to the original file and make changes without needing to create and reimport a new file.