Categories are not assigned to rules. Messages are assigned to categories,
and this can be done by rules. Here's another try at explaining how to set
this up:
Create as many categories as you have rules. Give each category a name which
will suggest to you which rule will assign messages to that category. For
example, if you have a rule named "FromTheBoss", you could create a category
"FromTheBoss". (Note: this does NOT create any assignment or other
relationship between category and rule!)
Now edit each rule. In the Select action dialog, add the action of "assign
it to the category..." In the bottom panel of the dialog, click the
underlined word "category" and from the list select the name which is
supposed to remind you of the name of the rule you are editing. (THIS is what
establishes the relationship between rule and category - but in YOUR mind
only, not intrinsically in Outlook.)
So, Rule 1 runs when its condition is met, performs whatever actions you
specified, and in addition, assigns the message to Category 1. Rule 2 runs
when its condition is met, performs its actions, and in addition, assigns the
message to Category 2, and so on. Whether a rule runs or not depends ONLY on
what you selected in the conditions dialog, not on any categories. If a
message ends up not assigned to any category, it means either a) one or more
of your rules do not have the assign category action checked, or b) if all
rules assign categories, then this message did not meet any of the conditions
of any rule.
You original objective, as I understood it, was to have a way of telling
which rule processed a particular message. How does my process help you
achieve this? You look at the category to which a message was assigned. If
it's Category 1, it was processed by rule 1; if cat. 2, then processed by
rule 2 and so forth. If you display the category column, you don't even have
to click to find out which rule ran. To edit that rule, you open the rules
dialog and scroll down to the rule name that assigned that category. That's
why the name of the categories must be chosen to give you a clue as to the
name of the rule that processed that message.
It is not possible to go from a message directly to editing a rule, because
in general a message could be processed by multiple rules. Which one would
you go to? But the above process can assign such a message to multiple
categories, so you could edit each of the several rules in turn.
BTW, the list of rules is not random, but in order of priority. In certain
situations, it may be essential that one rule runs before another, especially
for rules that have the "stop processing" action. Suppose you have a rule
that moves messages sent to a particular account into a "Later" folder, and
another that moves messages from your boss into the "Now" folder. If your
boss sends you a message to that account, your FromTheBoss rule better run
first.
You can change the displayed order by clicking the up-down arrows at the top
of the Rules dialog. So you could order them alphabetically, but this might
defeat some priority requirements.