when to use depends and when to use requires

Greetings,

I still don't know what are the proper guidelines to use Depends or Requires.
I had an example of a target a and target b, target a depends on b, b creates a few files, one of them is needed for target a. I used Depends here.
depending target a on target b didn't enforced the proper order, adding the relevant file to the dep list didn't worked, however, when I changed it into Requires,
the order was enforced.
from that I deduce that for code files which I need to use as part of another target I should use Requires while for the rest, I should use Depends.

am I right?

Dagg