Learn Turkish: Çok yemek kötü. - Eating a lot is bad.

The word yemek is actually the infinitive form of the verb 'to eat', which can translate as 'to eat' or 'eating'. Because eating is such a common action, the exact same word is also used as the noun for 'food'. Here, it is being used as a verbal noun, making the phrase çok yemek mean 'eating a lot'.

How does the -mek suffix work in this sentence?

The -mek suffix turns a verb into a noun. By leaving the verb in this dictionary form, you can use an action as the subject of a sentence. Just like in English where we say 'Eating a lot is bad' or 'To eat a lot is bad', Turkish uses the infinitive yemek as the main subject of the sentence.

Why does çok come before the verb instead of after it?

In Turkish, words that describe an action usually go right before the verb. So, to say 'eating a lot', you place çok (a lot / much) directly in front of the verbal noun yemek (eating).

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

Turkish doesn't have a separate word for 'is' or 'are' in simple descriptive sentences. You just state the subject (çok yemek) and follow it with the adjective describing it (kötü). The 'is' is naturally understood.