Hi Jae Won Lee,
The Floor Object (see attached image) is the one you might consider for this. It is an object which renders to the horizon. (Horizon means here the “infinite” ending of the object, or in Perspective terms, where the vanishing points would be.)
If you like you can move and rotate this object, as well use as many of them as you like.
To texture it, use a Shader or a large tiled Texture. As the Object has no UV information, you might prefer to use the “Flat” projection, or any other “non UVW” option. Camera Projection might be an idea as well.
If the horizon is a little bit “jaggy” you might check the Help Content about MIP/SAT: Reference CINEMA 4D> CINEMA 4D Prime> Material Manager> Material Properties / Material Editor
You headline of this thread “Requesting breakdown of a motion graphics piece” would be best placed in the “Request Tutorial” forum, if the whole process is of interest.
The Sky-Object is a second object with such qualities, but not flat—it is an infinite sphere.
All the best
Sassi