Well, that being said, lets get started then, eh?
Each of these will breakdown the general army strategy, the core units (that you will always see), the important units (ones you will likely see) and how you should, in general play against it. As always, play to your armies strength, not your opponents weakness. Control the game.
Kan wall is one of the 3 currently competitive Ork builds (the others being Wagon Spam and Green Tide). It is a tough army, with a high model count and plenty of decent shooting (for an Ork army at least). Killa Kanz have a Ballistic Skill of 3, which means they start to approach reliability with their shooting, and they often have a few squads of Loota, which can deal out lots of shots from far off. To back that up, typically they will have assault elements, such as a Deff Dread (as a Troops choice due to Big Mek) and/or Boyz. The Kans themselves, armed with Dreadnought Close Combat Weapons are no slouch in HtH either. This list offers a lot of balance, which is the typical hallmark of a competitive tourney list.
Killa Kans - The Armies namesake is the core of the army and you should expect to see 3 squads of 3 Kans each (for 9 Total). Killa Kans are AV 11 F and can have a variety of weapon options. Typically you will likely see Rokkit Launchas (Str 8, AP3, 24" range) or Grotzookas (Str 6, Ap 5, "18 Range. Blast. Heavy 2). Rokkits provide anti-tank/transport, while Grotzookas are pretty solid anti-infantry weapons. They also have DCCW's, so they can strike hard. Also remember that Big Mek's can repair them.
Big Mek - The Big Mek is the cornerstone of all Ork lists in this day and age, purely because of the the Kustom Force Field and its ability to give most of your army a cover save, even in the open. Considering the cheap but easy to kill slant for Orks, making them much harder to kill has a profound effect. Also, check with the TO before the game begins to see if that particular tourney uses 4+ cover saves for Kans, or 5+. Its a disputed rule on the KFF.
Deff Dread - The bigger, meaner, Deff Dread might be played. They can be fearsome in CC and add even more armour for you to deal with. Expensive though, so not everyone runs it.
Lootas - The best long range firepower in the Ork Codex, most lists will run between 15-30 Lootas, divided up. They can deal out a lot of damage in a single volley, so try to keep cover from them.
Grots - For 40 points, the Kan wall get area coverage early and an objective holder late. Since the Kans are likely to give them cover all game, they will typically be saving at 3++ to all your shooting, making them difficult to take down at range. Assault them if you can, but you might not make it there with all the walkers in the way.
Kan Wall is a balanced list and is very slow. This means they are naturally at a disadvantage against lopsided armies that are faster then them. Shooty Dark Eldar for example, or IG Gunline. That being said, it is a resilient list and is typically Very hard to table. Concentrate on taking down full squads of kans early, and do your best to whittle down their boy squads if possible, specifically whichever mob has the big mek in it. Remember that squads of vehicles treat stunned as shaken and count immobilized as destroyed. Keep up the pressure early and stay out of their reach. They will hurt you shooting, but don't have huge range.
Next week I will shift gears and talk about one of the few viable Vanilla SM lists: Vulkan Lists.