3D models can be from your imagination or from real world items. Today’s model is from the real world.
I modeled a picnic table from one that is available at Home Depot. I used the online photos in fspy to get the camera position. The fspy camera positions and the phone are then imported into Blender with an add-on. I then drew and aligned picnic table elements in Blender. When it was all done, I scaled it to real world sizes and added weathered wood materials. The materials were created with overlapping UVs. This allowed me to get decent resolution without using huge images.
The model is available at CGTrader.