Order of declaration and usage

Hi,
 
A beginner's question: Does the order in which resources are declared and
used matter? So for example, if I use a Property first in some triple, and
at the end of the file declare that Property, is that syntactically valid?
 
And what about the same question for objects, so first create a triple with
subject S, Property P, and object O, and then further down in the file
declare that object O?
 
Regards,
Hans