Thanks to everybody who answers our posts.
Hannes has this Material post which helped me understand where to put textures.
https://planetside.co.uk/forums/index.php/topic,22695.0.html
I found out about Internal Networks, you know where they hide the colors and good stuff you can change.
The bicycle in front looks good in other programs but not in Terragen.
Now i can import a grey colored object and assign textures in Terragen and get the bikes in the back.
Thank you all
Cool! Glad, you found the materials useful!