[...] This article will take the shortest, simplest, easiest-to-understand path in explaining all the aspects of ergativity and similar, at the cost of being as technically accurate as possible. That is not to say that it should be inaccurate—Just that it could perhaps be considered more along the lines of metaphorical rather than wholly literal.
You may be familiar with the concept of "subject" and "object" in grammar from school and/or elsewhere, but a definition will be supplied here regardless, to the relief of those un- or ex-familiar. The subject is that which does the action of the verb, whereas the object is that which undergoes the action of the verb. Take the following sentence as an example:
The cat eats the mouse.
The cat, who does the eating, is the subject, while the mouse, who is being eaten, is the object. Some verbs do not take an object.
The cat eats. The cat sleeps.
The verb "(to) eat" can take an object, or have the object left off, but the verb "(to) sleep" never has an object. "(To) Sleep" is intransitive, while "(to) eat" is ambitransitive. Some nouns can only be transitive.
The person feeds the cat.
The person feeds the cat a mouse.
The person feeds the mouse to the cat.
*The person feeds.
*The person feeds a mouse.