Learn Hardcore Turkish: Tarla geniş.

Tarla means “field” and acts as the subject of the sentence. In Turkish, the nominative case (used for subjects) is unmarked in the singular, so there’s no suffix on Tarla.

Where is the verb “to be” in Tarla geniş?

In the present tense, the copula olmak (“to be”) is dropped (zero copula). You simply put the noun + adjective. If you want to be extra formal or written, you can add -dir: Tarla geniştir.

How do I turn Tarla geniş into a question like “Is the field wide?”?

You add the question particle -mı/–mi/–mu/–mü right after the adjective (harmonizing vowels) and use rising intonation:
Tarla geniş mi?

Why is the adjective geniş placed after Tarla, whereas in English we say “wide field”?

Here geniş is a predicative adjective (“is wide”), so it follows the noun. When an adjective modifies a noun directly (attributive), it comes before:
geniş tarla (“wide field” as a noun phrase)

How do I say “a field is wide” instead of “the field is wide”?

Turkish has no indefinite article like “a.” Context often suffices. If you want to be explicit, add bir before the noun:
Bir tarla geniş.