There are a few certain differences between doing a 3D print and using a 3D pen.
Using a 3D pen is something that you do more manually with your hands which can be used to add small details that you couldn’t with a 3D printer. Or, you can use it to make a repair to something to get it to hold together. You can also make something that is for random everyday use or a decoration.
Using a 3D printer would require other skills that you wouldn’t really need for a 3D pen. You would need a lot more filament than a 3D pen would.
Filament is the plastic material that you would need to operate the printer or pen. Filaments can be solid colors or some can be transparent. It is plastic and is easy to paint over if you run out of a certain color. There’s also filament that can be two colors, there’s glow in the dark ones, you name it. Over time, filament can be a bit expensive.