It's very possible to make your own 3d models (or grab other people's stuff) in blender and import to Daz.
Once in daz, you'll have to assign relevant materials to all the surface areas. But there be dragons...
What's that? Your blender model didn't have surfaces assigned? oh well, back to blender you go, and this time do it right.
What's that? you didn't have UV maps already created? oh well, back to blender, and surely you'll learn from your mistakes.
What's that? you don't have textures that match the UV map? you better get started on learning how to paint textures! Or learn to do direct-to-surface painting in Substance Painter / Zbrush / etc etc.
All facetious comments aside: The easiest cases are objects that do not need complex textures - basic geometric objects, or smooth painted machinery surfaces, or some types of architectural works. You can also cheat for some surface features by adding decals.
But the fact is that creating non-shit-tier 3d content is a whole job of work. Professionals take months to get good at it.