How to sort messages?

How to sort messages?

I'm a novice programmer in PHP.
I have a simple messaging site with users in one table and another table
with messages:
(date, from user, to users, message, primary key, subject).
First of all, I'm not sure this is the right way to have messages stored,
so please tell me.
What I'm confused about is the display of the messages.
I want the page script to:
connect to the database
authenticate user
go through all messages in messages table (good up to here)
go through the to users field, see if user is one of them (splits it up
into array)
if it is:
check to see if any other messages have the same users in their to users
field
if it is:
group it with the others with the same users in their to users field
(possibly in a second dimension of a multidimensional array)
else:
put it into a new "group" (with the next first dimension of a
multidimensional array)
Then, I'll display only the ones of the first dimension of the
multidimensional array, and when clicked will display the rest of the
messages (all the second dimensions of a multidimensional array) in
another place.
If somebody could help me with these steps with some bits of code or links
to a website that could help, please do so.
Please help! I really have no clue how to do this - I've tried a few times
but it's taken so much time and effort, I think I'll need some help.
Thanks in advance.