There are effectively a few different ways about creating 3D animation and models. Once you’ve learned the basics you’ll develop your own approach to animation, likely using the following methods.
Splines are an entity in rendering software that is uses to delineate a shape which is then brought out in three dimensions. If you draw, say, a flat rectangle in a spline, you can then fold, shape and alter the rectangle into a three dimensional shape. Think of this as a sort of origami on your computer, except that you can create as many paper sides and polygons as you want to finish your piece.
Sculpting a Basic Shape
One of the more common methods for creating objects in 3D is actually to take a sphere, cylinder or rectangle and to shape, pull, push and sculpt it to your specifications. This is a good idea if you need to create something like a realistic face or softer surfaces. This is a lot like sculpting in polymer clay. Different programs include different tools, but most will include some kind of “magnet” tool to pull on your polygonal surfaces and “extrude” to pop whole polygons in and out of the shape.
One of the easiest ways for beginners to get started in 3D rendering is to take a drawing or photo of the front and side of the object they want to model and then shape and spline to the specifications of the object. From there, the object can be fine-tuned, but the basic shape will be there from the start.
From there, learning the rendering software and 3D animation will involve learning how to create “skeletons” to control the 3D objects, how to use lighting and cameras to create compelling animations and so on, but it all starts with basic modeling skills.