Different printers use different materials. Some 3d printers can only form Wax; and I am not saying wax is bad, it's probably one of the best out there, along with ceramics and other plastic variants.
In big companies and industries people definitely use melted metal, but I don't know what you need it for? If it's just home use then start slow and not immediately with metal; it can be risky if you don't already have experience working in that environment, so try not to get involved.
Technology is going to improve for home 3d printers, you'll be able to perform tasks with sandstone and what not.
Metals are also used for printing Airplane wings and Guns! Yeah, it's scary but true. The only big task is the environment for melting the metal; that's a lot of planning with different devices and a lot of work and precaution. Just stick with basic material as of now like Wax, ceramics etc. and you should be good, best of luck!