For a 3D printer to work there are 3 things which are needed
Firmware is what allows the printer to read the sliced file and print the object. This is a part which will 99% of the time come with the printer and you will not need to do anything.
This is used to convert a 3D object that was created in the design software or from a downloaded file into what is called a G-Code file (a.k.a GPS for the 3D printer). This file allows for objects to be 3D-printed. Some common slicing softwares are CURA or Slic3r