Creating in 3D
Most people are used to creating in 2D. Drawing, painting, writing, even photography can be considered 2D art forms. But most people don't think of themselves as 3D creators, even though we all live, work, and play in 3D space every day. If you have ever rearranged your living space, built furniture, played with building blocks, carved wood, decorated a cake, sculpted with clay, even arranged flowers, you've created in 3D.
Creating in 3D just means working creatively in a space where objects have 3 dimensions: height, width, and depth.
Digital 3D tools
If you've played video games, there's a strong chance that you've already used 3D creative tools. In Fortnite, every time you frantically build a structure to defend from other players, you're using 3D tools to create. Even destroying other players structures is part of the creative toolkit.
The toolkit that Fortnite provides is limited, because the goal is to create something functional and fast, not necessarily something beautiful. Most general 3D tools are not limited in this way, they want you to be able to create anything you can imagine, and that usually means more tools, more options, and more complexity.
To help simplify the process it's often useful to break up the 3D process into a sequence of steps, also known as a pipeline.