The patches include changes to the environment and characters.Patch 2.4 will introduce Sunwell Isle along with the new five-person instance, the Magister's Terrace, and a twenty-five person raid, the Sunwell Plateau will be added to the game. These will be accessible to high level players, so it gives rookies something to look forward to, but not a new zone right away. There will also be new regular quests and repeatable daily quests that are excellent sources of gold and reputation in the endgame.
The changes to characters can be difficult to cope with at time. We all select our characters based on their abilities and grow accustomed to what they are capable of. Patches often change spells and abilities which, in turn, modifies how they affect game play. Some of the changes are beneficial to some classes while weakening others. These "buffs" and "nerfs" are a source of considerable controversy but are implemented as the developers see fit for game balance. Your class will change once patch 2.4 is released. Blizzard keeps a list of potential changes that are being tested on the PTR.
The developers at Blizzard ask for our help in testing and tuning their proposed changes. The Public Test Realm gives players a chance to sneak preview the coming changes and allows Blizzard to see how their changes affect game play and game balance. Patch 2.4 is using a progressive testing method where changes are introduced and tweaked over time. Some of these have been well accepted, others have caused anger and outcry among the players.
Everyone with an active account is invited to play on the PTR and give their feedback. Ordinarily, to get to the public test realm you must copy or create a character on the public server. Currently the test realm is only accepting copies of existing characters, so you can't make the new characters on the test realm. You will have to select either to copy your character to a PvP or a PvE server. It usually takes several hours for a character to copy
You will also need to download the test client. When you first download the patch, there will likely be several additional patches. It takes some time. With progressive testing, you may have to patch several times over the course of the test. Once it's you've got the public test client on you computer you can go to the test ream by clicking public test on the launch screen instead of play. Blizzard has opened up an additional test realm to prepare for the upcoming worldwide arena tournament. Our Zach Yonzon posted a step by step guide for accessing the Tournament Test Realm.
Once you're on the PTR, you can check out the items and content, and give Blizzard your feedback on any of it. This helps the developers to hone the game. Blizzard hosts a forum for the test realm. Players can go here to give their suggestions, voice their grievances, and discuss the changes with other testers. The rules for this forum can be found here.
No changes on the PTR are guaranteed to go "live" into the regular servers. Testing is the prefect time to give feedback, but not time to panic about changes. There are usually smaller patches between the major ones with fewer sweeping changes. These usually don't even make it onto the PTR.
Technically, the Burning Crusade was patch 2.0 and Wrath of the Lich King will be patch 3.0. Those were major content expansions, but in effect are little more than gigantic patches. Prior to the Burning Crusade the maximum level was 60 and Blood Elves and Draenei were not playable races. The Burning Crusade brought along Jewelcrafting as a profession and an extensive addition to content and storyline. We're working diligently to bring all of the latest information and speculation for Wrath of the Lich King.
Patch 2.4 is definitely coming. No one can say for sure when either patch 2.4 or Wrath of the Lich King will be released. Not even Blizzard. The typical response the developers give when probed about a release date is "when it's ready." You'll know it's patch day because when you go to log in and the first screen you come to will say "Patch Required." The patch is not optional, all computers with WoW installed must be updated once the patch goes live in order for players to log on. Blizzard may make the patch available a few days or weeks ahead of when it goes live to reduce the stress of downloading.
In the meantime, be patient along with the rest of us, and keep checking out patch 2.4 coverage so you'll know what to expect. Feel free to mosey on over to the PTR and see what the buzz is about.
Edit: Removed free reference.