Learn Finnish: Vaimo ei laita ruokaa nyt. - The wife is not making food now.

In Finnish, if a sentence is negative (like here with ei), the object of the sentence must be in the partitive case. To do this, the basic word ruoka gets an extra -a at the end to become ruokaa.

Why is the verb laita instead of the basic form laittaa?

In negative sentences, the main verb takes a short stem form. You find this form by taking the "I" form of the verb (laitan) and removing the -n. Notice that the strong double tt in laittaa weakens to a single t in laita. This spelling change is a rule called consonant gradation.

Doesn't laittaa usually mean "to put"? Why does it mean "making" here?

You are right, laittaa very often translates to "to put" in English. However, laittaa ruokaa is a very common set phrase in Finnish that specifically means "to make food" or "to cook".

How do we know it translates to "the wife" when there is no word for "the" in the sentence?

Finnish doesn't have articles like "a" or "the". The word vaimo can mean either "a wife" or "the wife" depending entirely on the context. In this sentence, "the wife" is simply the most natural translation.