Can't understand mesh creation

I’ve been searching for a tutorial on creating meshes for Unreal Engine. I have only been able to find tutorials on how to export meshes to UE4. As I understand, complicated meshes cannot be created on UE4, and are created on softwares like Blender.
I saw on a popular YouTube tutorial that materials can be assigned to a predetermined area of a mesh soon after importing the asset into the Engine. I assume this ‘determining which material applies where’ is done before the asset is imported, in Blender, but I have seen the entire official Blender tutorial on YouTube and found nothing on this.

Can someone please explain, or share a link to a tutorial that explains, how materials are assigned to a certain part/group of parts of one whole static mesh, even if this is done on other softwares like Blender?
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You will need a 3d suite to create complex meshes.

In short, in the modelling app you either assign an ID or a material to each face as needed.

3ds Max: https://www.youtube.com/watch?v=DIk6ulOMDvo

Blender: https://www.youtube.com/watch?v=G5rRdej3NKw

Can’t vouch on the quality of the Blender tut (not a Blender guy) but it seems to add up at a glance.

Thank you. I’m sure these will be helpful.