Rendering is making a near-photorealistic picture of a 3D design, like CGI in movies. Here's an example render of a jumping robot prototype:

In the past, we've finished a microrobot design in a 2D layout tool, extruded the 2D layers into 3D geometry and saved it in the STL 3D file format, then used the free and open source program Blender to render the STL file. We have a video tutorial on how to do this here: https://drive.google.com/drive/folders/1fBLqA_zgTE0LRyE9Brb9oQ1m0K54KaO4?usp=sharing

Daniel Teal originally wrote the program gdsiistl to create an STL file from a GDSII layout, but it's been copied to a group GitHub repository at https://github.com/PisterLab/gdsiistl and is part of the larger library of programs and scripts to programmatically create designs at https://github.com/PisterLab/microrobot_library.

Blender is available here (Windows/macOS/Linux): https://www.blender.org/