Learn Hardcore Afrikaans: Die hele tuin is skoon.

Die is the definite article the in Afrikaans. It marks that we’re talking about a specific garden. Unlike English, this article doesn’t change form (no gender or number variation).

How would I say “a whole garden is clean” instead of “the whole garden is clean”?

Use the indefinite article ’n (pronounced roughly “uhn”):

’n hele tuin is skoon

What exactly does hele mean here, and how is it different from heel?

hele (with -e) is an attributive adjective meaning whole or entire before a noun (as in “the entire garden”).
heel (no -e) is an uninflected adverb meaning very or quite when placed before adjectives or adverbs (e.g. heel mooi = “very beautiful”).

Why is the adjective skoon not given an -e here?

Because skoon is functioning as a predicate adjective (“is clean”). Predicate adjectives follow the verb is and stay in their base form—no -e ending. (Attributively, it would be skone tuin = “clean garden.”)

How would I say “the clean garden” as a noun phrase (attributive use)?

You put the adjective before the noun and add -e:

die skone tuin

Why is the verb always is? Don’t verbs change with person or number?

In Afrikaans, present-tense verbs do not conjugate for person or number. is is used for I, you, he, we, they, etc.

How do I turn the statement into a question like “Is the whole garden clean?”?

Simply invert the verb and subject:

Is die hele tuin skoon?

What about past tense—how do I say “The whole garden was clean”?

The past-tense form of is is was:

Die hele tuin was skoon

How do you pronounce tuin?

tuin is pronounced [tœyn], similar to English toyn (rhymes with coin). The ui is a diphthong uncommon in English but akin to Dutch ui.

If I want to talk about multiple gardens, how do I say “the whole gardens are clean”?

Plural of tuin is tuine, and the verb & adjective remain unchanged:

Die hele tuine is skoon