Google "3d printing toolchain" or "3d printing software toolchain" for an overview of how to get from design to a printed model.

In short, you go from a design program like AutoCAD, or Sketchup, MeshBuilder or any one of a number of programs, to an STL file that is processed by a slicing program such as Slic3r, Cura or Kisslicer to create gcode specific to your printer. Send the gcode file to your printer and your piece will start to appear.

I'm not sure what question you're asking regarding robotic. Are you asking how to design and build robots using 3D printing? Maybe ask on one of the robot building forums, like letsmakerobots.com. Try searching thingiverse.com for robots to see if there's a design on there you can start with (fair warning: a lot will be toys, not buildable robots).