According to Merriam-Webster.com, 3D printing is "the manufacturing of solid objects by the deposition of layers of materials (such as plastic) in accordance with specifications that are stored and displayed in electronic form as digital model."
It might be easier to ask what can't be done with 3D modeling. 3D models can have medical, engineering, art, architecture, gaming, manufacturing and marketing applications, the sky is the limit. Actually the sky is not the limit. 3D printing in space offers NASA a quick and inexpensive way to manufacture parts on-site and on-demand. For more information on how 3D printing is being used, please see the Special Topics page.
There is no single answer for how long it takes to complete a 3D model. Factors include: the software used, the design and complexity of the model, the size of the model, the printer equipment used to create the model. Some objects could be created in an hour, while others take many hours or even days.
The Anet A8 printer was reputed to be the most popular 3D printer until the fall of 2018. The Anet A8 is still an affordable, very popular printer. One thing to note, there have been a number of reports of A8 printers catching fire. Just as you should never leave an unattended stove or iron on, Never leave an operating/heating printer of any make or model completely unattended.