Ania, as you mentioned, the different organizations have different rules for earning Qs and Points if they are required.
I believe the rules outlined by Stacy apply to AKC.
I run CPE (Canine Performance Events) Agility and their rules are different. They actually have their rule book on their website,
http://www.k9cpe.com/rcall2007.htm, for anyone to view. (I wish AKC's rules were that easy to find. I've been looking for them.)
In CPE, at least at Levels 1 - 5, you only need Q's to advance. I'm not 100% certain about their Championship (C) level.
After about 1 year of training, and you'll be AMAZED at how much you learn in a year, Edan and I entered our first CPE trial. At level 1 you need 2 Qs in Standard agility and 1 Q in all the games to advance from Level 1 to Level 2. They also have what I've taken to calling "minor titles" between levels; those are the ones you see in my signature. These signify that you completed all the skills for a particular grouping of games or standard within a given experience level. (This is all in the rulebook I linked you to.)
To Q in CPE, you just have to be under the course time and not go over the max faults allowed for your level (10 fault points at Levels 1 - 4).
Because of the structure of the levels in CPE, it is VERY easy for a complete novice to Q and earn titles early on which helps build both the Handler's and Dog's confidence.
By the way - NADAC, TDAA, USDAA and CPE all have their rules online for anyone to view. I know I've been unsuccessful finding the official AKC rules.