Adding texture (pictures,videos) to 3D in videos.

You need to vet your trainers. That Photoshop tutorial was pretty awful.

In After Effects projecting an image on extruded text is fairly straightforward if you use the C4D or Ray-traced rendering engine, but be warned that it is going to take an incredibly long time to render. The technique is to put an image in front of a spotlight, set light transmission to 100% and throw the image on the extruded layer in the same way you would cast a shadow. It's called projection.

A much easier and faster to render solution would be to spend an hour or so learning how to use C4D lite, which comes with After Effects and extrude and texture your text there. Keep the first project simple and you should not have much trouble.  For either technique, you could start by using the Search Help field in the top right corner of After Effects. It's a very good resource for anyone, especially those just starting out with the app. AE is about a thousand times more complicated than Photoshop.

Here is the basic workflow using C4D lite.

1. Create a new composition using Classic 3D rendering.
2. Add a text layer
3. Add a camera
4. Position the camera and the text layer
5. Choose File>Expoort>MAXON Cinema 4D Exporter
6. Choose Editable Text or Text to shape when exporting the file
7. Save the file in the project folder
8. Import the saved text file to your After Effects project
9. Add the file to the Composition timeline
10. Turn off the camera and text layer (you may need the camera later so don't delete it
11. Inside C4D pick one of the textures that are applied to your text layer
12. Add an image or video to use as a texture in the Color section of the Texture Editor
13. Make sure the texture is assigned to the faces you want to be textured
14. Save the C4D file
15. Back in After Effects, you'll see your extruded text layer with a grid over it
16. Change the render setting in the Cineware Effects Panel to Stanard Final

That's all there is to it. You will need to do some homework to learn how to assign textures to various faces, adjust the extrusion and do other things. If you animated your camera in After Effects you will still have the same animation, or you can choose to modify the camera move in AE and use the Comp Camera in Cineware. It's all pretty easy, once you do your homework.

If I were teaching a class on this we would probably spend about 4 or 5 days going over the possibilities and getting used to the interface, then I would give the students about 3 days to create something that would wow me. Three days of homework translates to about 4 or 5 hours...

Let us know if you have any other questions. There are some fair tutorials out there on this workflow but I don't know of a really great one. I would suggest starting on the Maxon website, and once again, make sure you vet your trainers. There are more amateurs giving poor advice and inefficient workflows than there are pros demonstrating good ways of doing all things AE and C4D.