How does the ablative case work?

The easiest way to explain it is that it is the 'adverbial' case. This means that it will always tell us something more about how an action (described by the verb) took place.

One of the simplest examples to demonstrate this is the following sentence:

puer militem gladio necavit

If the sentence had lacked the ablative 'gladio' then we would not have known how the boy killed the soldier; as it is, we are told that the boy killed the soldier 'with a sword'.

The ablative thus provides more information about the action taking place, information that is often interesting and extremely useful in understanding the text.

If you get stuck about how a noun in the ablative case fits into the sentence, just remember that it will always be answering one of the four following questions about how the action took place: 'how', 'when', 'where' or 'why'.

When you ask yourself which of these four the ablative is answering, it will soon be obvious which one and will be then much clearer how you should translate it.