Good question. Die kompos means the compost, referring to some specific compost already known from context.
If you remove die, you get:
That can sound more general or less specifically identified, depending on context.
So the sentence with die suggests a particular compost, not compost in general.
Because Afrikaans and English are related Germanic languages, so some very common words look alike.
Here, is is the present tense of wees (to be):
A nice feature of Afrikaans is that the verb does not change form for different persons in the present tense the way English does.
Tuin usually means garden, but in some contexts English speakers might translate it as yard depending on how the outdoor space is understood.
So in die tuin is most naturally:
But if the real-life context is a house and its outdoor area, an English speaker might sometimes think of it as in the yard.
Tuin has a vowel sound that does not match English perfectly, so it can be tricky.
A rough guide is:
If you need a very rough approximation, you can think of it as something a bit like t-oyn or t-ain, but neither is exact. The important thing is that the ui is a special Afrikaans/Dutch-type diphthong.
Yes, you could, but it changes the nuance slightly.
Afrikaans often uses position verbs like lê, staan, and sit, but beginners will very often first learn the simpler pattern with is.