You can know the difference between a 2D and a 3D Animation just by the appearance, here is an image of the same character in 2D(Left) and 3D(Right).
The image is by a 3rd party I don’t hold any rights for it
How it’s made
In 2D Animation the animator needs to have strong drawing skills because 2D Animation requires you to draw every frame which makes it really on drawing, these drawings have minor changes which, when arranged in sequence creates a motion picture due to (perception of vision). You only need to draw what is seen by the viewer (example: You don’t need to draw the eyeball if the eyes are closed) These days 2D Animation is created in software (Flash, After Effect, Toonboom Harmony), with the help of digital tablets (pen and tablet), some software these days don’t require you to draw every frame, you only need to draw the keyframes and the software creates in-between by itself, the Animation is tweaked with the help of a graph editor.
In 3D Animation the animator works in a 3D workspace know as the viewport, where he controls the environment, component, and objects with 3 axes, X, Y, Z, these axes position property vary depending on the software preference and default settings. You can move your animated subject by using the controls provided after rigging, but things that are not in the view (captured by the camera) still exist, because of the 3D properties (example: The eyes are still present but not directly visible due to overlapping of a mesh structure). The Animation is tweaked with the help of the graph editor, which is available in every 3D Animation software.
If you plan to learn Animation as a course and choose to make it your life, I would suggest you learn both, learning both will help you in understanding the two in a relative manner, if you are planning to learn it has a hobby you can do the same or try out 2D and 3D and choose which you are comfortable with it. Stay tuned to read more about Animation related stuff, you can subscribe via email to receive emails over new articles every week. Thank you for reading.