Die sleutelgat is klein.

Here die is the definite article, so it means the.

A few useful points:

• die is used with singular nouns and plural nouns
• it does not change for gender, because Afrikaans does not have grammatical gender like German does

So die sleutelgat means the keyhole.

Afrikaans often writes compound nouns as a single word.

So:

• sleutel = key
• gat = hole
• sleutelgat = keyhole

This is very common in Afrikaans. If English uses a compound such as bedroom, toothbrush, or keyhole, Afrikaans will often write it as one word too.

It is made from two nouns:

• sleutel = key
• gat = hole

Together they form sleutelgat, literally key-hole.

In Afrikaans compounds, the last part usually tells you the basic thing it is. So a sleutelgat is a kind of gat.

This is normal Afrikaans main-clause word order:

• Die sleutelgat = subject
• is = verb
• klein = adjective/complement

So the pattern is:

subject + verb + complement

In this simple sentence, Afrikaans looks very similar to English:

• The keyhole is small
• Die sleutelgat is klein

Because klein comes after is, where it is used predicatively.

After a linking verb such as is, adjectives normally stay in their basic form:

• Die sleutelgat is klein.

But before a noun, Afrikaans often uses an adjectival ending:

• die klein sleutelgat = the small keyhole

So:

• after is: klein
• before the noun: often also klein here, with no extra ending in this case

Afrikaans adjective endings depend on position and noun type, so the form before a noun can sometimes be different, but in this sentence klein stays simple.

Yes, very much so. is is the present-tense singular form of to be.

So:

• Die sleutelgat is klein. = The keyhole is small.

Afrikaans uses is in this kind of sentence just as English uses is.

No. Afrikaans does not have grammatical gender in the way many European languages do.

That means:

• sleutelgat is not masculine, feminine, or neuter in a way you need to memorize for articles
• the article stays die
• adjectives and verbs do not change because of noun gender

This makes sentences like this easier to build than in some other languages.

You would say:

Die sleutelgat is nie klein nie.

Afrikaans usually uses a double nie for negation:

• the first nie comes after the verb or later in the clause
• the second nie comes at the end of the clause

So:

• is klein → is nie klein nie

This double-negation pattern is one of the most important things to learn in Afrikaans.

A rough English-friendly guide is:

SLAY-tul-khat

A few notes:

• sleu- has a vowel sound that does not match English perfectly
• the g in gat is the throaty Afrikaans g, like the ch in Scottish loch or German Bach
• the stress is usually near the beginning: SLEU-tel-gat

So an approximate pronunciation is helpful at first, but listening to native audio is the best way to learn it accurately.

A rough approximation is:

kline

The vowel is not exactly the same as in English, but that is a useful starting point.

Also:

• the k and l are clear and crisp
• the word is one syllable

So klein is short and simple in speech.

Yes, but then the meaning changes from the keyhole to a keyhole.

• Die sleutelgat is klein. = The keyhole is small.
• ’n sleutelgat is klein. = A keyhole is small.

So the grammar still works, but the sentence becomes less specific.