You're in the download and install forum, would you say that your topic is "how to get going with 3D in Photoshop?". If it is I can move the topic over to that forum.
In the meantime, the very basic version is that in Photoshop you can make a 3D layer from an external model. I read that these files can be brought in as a 3D layer:
DAE (Collada), OBJ, 3DS, U3D, and KMZ
Really, KMZ is just zipped Collada anyway. I haven't tried the other ones much, I would usually use Collada (DAE).
Collada is an XML format, and unusual in a particular way. As it's XML you could create any kind of attribute you can imagine, that may not be possible to import into other programs that haven't heard of that attribute. It's not unusual to find that programs can export to Collada but not import from it.
That aside, if you have a 3D model and can export DAE, OBJ, 3DS, or KMZ, you can make a 3D layer from it in Photoshop.
Here's an article on getting things in and out of Photoshop in 3D:
If you didn't already look at it, you should check out Adobe Dimension (formally called Project Felix). It can make more elaborate 3D scenes quicker than Photoshop:
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Photoshop does not synthesize a depth buffer and that is that. You need other, much more expensive tools for that such as photogrammetry tools or compositing programs liek Nuke.
I'm not sure what synthesizing a depth buffer is, but you can manipulate 3D models to place them into your scene, and you can rasterize the 3D layer if you want to edit the bitmap version of the model from that viewpoint. In this picture I imported a Collada file (the woman), made two copes of the 3D layer, adjusted them to different views, and rasterized them so that I could delete the shadow where it hits the car.
I'm definitely not a Photoshop expert, but using 3D models in a PSD seems to be easy enough.
One neat thing is that as you rotate the model you see the ground plane grid, and it's easy to make it line up with the perspective of the photo.