Unity is a Game Engine that allows you to create interactive 2D and 3D-setups that react to some sort of input (although one could easily make non-interactive things with it as well). Because it was made for Games most existing tutorials are traditionally geared towards a gaming crowd, this site aims to re-frame the Game Engine more from an art-perspective.
If you think about 3D-software you could put them into mainly three boxes:
|CAD-software||for modelling parts/geometry that can be manufactured||(OpenSCAD, FreeCAD, Autodesk AutoCAD, Autodesk Inventor, Rhino, pythonOCC, etc)|
|3D-Software||for creating Animations/Renderings, often for Film, Design or Architecture||(Blender, Autodesk Maya, Maxon Cinema4D, etc)|
|Game Engines||for creating realtime interactive stuff||(Unity, Godot, Processing, etc)|
So CAD-Software is about creating geometry for manufacturing, traditional 3D-Software is about rendering images for visualization and film and Game Engines are about creating 3D-imagery in realtime, often reacting to the input of one or more users.
This realtime aspect is also what makes Game Engines a bit challenging, because all calculations the Engine does must be made in time for every single image (Frame) the Engine produces – otherwise the image would stutter. If this happens one solution would be to throw a faster computer onto the problem – but often the more elegant solution is to make the code more efficient or to cheat a little bit (so instead of doing physically accurate light calculations, one could do something faster that achieves similar results).
Unity is by far not the only Game engine one could use, for simple 2D-things or to learn programming something more basic like Processing could be more straightforward. Unity isn't open source, so if you are lucky enough that your work gives you a certain amount of money, you'd have to pay a license fee – if you are looking for a good open source alternative I recommend looking at the Godot Engine which has gained a lot of traction during the last two years.
Unity allows you to create interactive programmes that run on Linux, Windows, Mac, Android or in the Webbrowser. For an art installation you could use an old laptop, connect it to speakers and a display or a projector, add some sensors and have a interactive artwork.