Hello, let me see if I can help:
1: Lootaz are their own unit in the same way that a squad of Immortals and a squad of Necron Warriors are their own separate units. This means that you should ignore the fact that they have the same profile - they are in all respects entirely different units with their own squad sizes, upgrades, and weapons options.
2: Ard Boyz is the name of the upgrade that improves the armor save of 1 unit of Ork Boyz [the troops choice] per army. So, if you field an army of Orks, and include at least one squad of Ork Boys as a troops choice, a maximum of 1 of your Ork Boyz units can take this upgrade and boost their armor save as a result.
3: Kommandos and Burnas are two entirely separate unit choices in the same way that Immortals and Warriors are two separate unit choices. Kommandos can take a burna as a weapon upgrade, but you should not confuse this option with the unit entry Burna Boyz, which is an entire unit of models carrying burnas. Again, Burnas generally refers to the unit called Burna Boyz, and burnas [lower case] generally refers to the weapon option which certain Ork units have access to.
Hope that helps!