Most home 3D printers use PLA or ABS plastic. Professional printers can use all sorts of materials, from metal to organic filament. Some printers use a liquid resin, which is much more difficult to handle. As a beginner, use PLA. It's non-toxic, made mostly of cornstarch and sugarcane, handles easily and is inexpensive. However, it's more sensitive to heat, so don't leave your 3D prints on the dashboard of a car on a hot day.  For a more detailed explanation of the different materials check out our best filament article.