Proper name is X-Cam not “xcam” or “x Cam” so we are clear.
X-Cam is obsolete! :(
The developers are no longer continuing the development, they let its homepage domain expire, it wasn't updated for 64bit arma3, X-Cam was abandoned. On 09-07-17 arma3 v1.74 update broke x-cam as you cannot move objects anymore.
Obj → nPro → give proper name → OK
Obj → sPro → your current project name should be highlighted → Save
Obj → lPro → choose project name → Load
Objects library is where all the config.cpp object classes are stored, without this library you cannot see and obviously place any objects.
Objects library is global, when you build the library it will remain there when you restart arma3 / x-cam.
When you start x-cam first time with CUP you need to rebuild the object library.
Set → ROL (rebuild object library) → load whole library → choose black (not blue) CUP A1 or CUP A2 etc class types → Rebuild
Now the black class type turn into blue and are available in x-cam.
You need to be in the definition file mode (or something).
Obj → Load → Definition File → close
Now you are in that mode, now just click CBF → OK, terrain builder file is created in arma 3 root directory and the file name is “<TERRAIN-NAME>_<PROJECT-NAME>.txt”.
Now you can import this file into terrain builder.
How do I get x-cam working with 64bit ArmA 3?
This quick guide assumes you already have X-Cam installed and working with the 32bit version of ArmA 3, if you do not then please run through X-Cam's install instructions prior following this guide and validate it is working with the 32bit version of the game first.