Learn Spanish (Latin America): ¿Quién ha hecho este desorden?

Hecho is the irregular past participle of hacer (to make or to do). Because it is irregular, it doesn't follow the normal rule of adding -ado or -ido. It is one of the most common irregulars you will need to memorize!

Why is the verb ha in the singular form if we don't know how many people made the mess?

In Spanish, the question word quién (who) is singular, so it takes the singular verb ha. If you already suspected that multiple people made the mess, you would use the plural form quiénes and ask ¿Quiénes han hecho este desorden?.

Why do we use este instead of esto for the word "this"?

We use este because it comes right before a masculine singular noun, which in this case is desorden. You only use esto when referring to an abstract idea or an unidentified object, never right next to the specific noun it describes.

Does the word desorden only mean a physical mess?

It can mean a physical mess, but desorden also means disorder. It can refer to chaos, a lack of organization, or a disruption. In the context of a messy room, though, it perfectly translates to a mess.