Learn Turkish: Yemek yapmak zor değil.

In Turkish, you can use the dictionary form (infinitive) of a verb as a noun. By adding the suffix -mak to the root yap, "to make" becomes the concept of "making." So, yemek yapmak translates to "to make food" or "cooking," which acts as the subject of the sentence.

Doesn't yemek mean "to eat"? Why does it mean "cooking" here?

Yemek is a very common double-duty word: it can be the infinitive verb "to eat" OR the noun "food" or "meal." In this sentence, it's the noun. The phrase yemek yapmak literally means "to make food," which is the standard way to say "cooking" in Turkish.

Why do we use değil for "not" instead of adding a negative suffix like -me or -ma?

You only use suffixes like -me or -ma directly on verbs to negate actions (like "I don't cook"). Here, you are negating the adjective zor (hard). To say a noun or adjective is "not" something, you must use the separate word değil.

Where is the word for "is" in this sentence?

Turkish doesn't use a separate word for "is." When describing something in the third person ("cooking is..."), you simply state the subject and its description. Zor değil literally means "hard not," which translates perfectly to "is not hard." You could add a "to be" suffix at the very end (zor değildir) for formal writing, but it is usually dropped in everyday speech.