Explanation stored procedure : I Am trying to understand a stored procedure, but i don't get it. I'm totally new to stored procedures. I have ordered a book about t-sql but it didn't arrived yet. I'm litterally stuck.

Can someone please explain to me what the following stored procedure, exactly does?

[Stored procedure][1]

I know that ALTER stands for, modifying the stored procedure, 
@ Region and @ State are the parameters. 
Begin is where the stored procedure starts
When do you have to use '' , like in the first select statement? 
What exaclty is the LO. and PR. ?


  [1]: http://i.stack.imgur.com/xQP1G.png