An object number is simply a whole number, like 1, 5 or 678
Every DB object, be it a loaded model, a sphere, a box, e.t.c is referenced by a number.
examples:
LOAD OBJECT "man.x",1
this will load the file into object number 1
MAKE OBJECT CUBE 25,50
this will make object 25, which will be a cube of size 50 units
These object numbers can then be used so you can move them around with commands like:
MOVE OBJECT 1,5
this will move our man object (1), 5 units forward.
I think you need to go through some beginner tutorials...
Boo!