Sowel die opwarming as die afkoeloefening is belangrik.

It means both ... and ....

So:

• Sowel die opwarming as die afkoeloefening
  = Both the warm-up and the cool-down exercise

This is a common Afrikaans pairing used to connect two things that are both true or both included.

Afrikaans repeats the definite article before each noun here:

• die opwarming
• die afkoeloefening

So sowel die X as die Y is the normal pattern for both the X and the Y.

English can sometimes sound natural with one the covering both nouns, but Afrikaans often repeats die when each item is named separately.

Because in Afrikaans, is is used for all persons and numbers in the present tense of wees (to be).

So Afrikaans does not change the verb the way English does:

• English: it is / they are
• Afrikaans: dit is / hulle is

That means is is correct whether the subject is singular or plural.

Opwarming means warm-up or warming up.

It comes from the verb opwarm, meaning to warm up.
The ending -ing often turns a verb into a noun, similar to -ing forms in English.

So:

• opwarm = to warm up
• opwarming = warm-up / warming up

In this sentence, it is being used as a noun.

Afkoeloefening means cool-down exercise.

Afrikaans very often forms compound nouns by writing them as one word, where English would often use two words or a hyphen.

So this is built from:

• afkoel = cool down
• oefening = exercise

Together:

• afkoeloefening = cool-down exercise

This is very typical Afrikaans spelling: compounds are usually written together.

Here oefening means exercise.

Depending on context, oefening can also mean:

• practice
• training exercise
• drill

In this sentence, because it is connected with warming up and cooling down, exercise is the most natural meaning.

Because Afrikaans adjectives used after the verb usually stay in their basic form.

Here:

• is belangrik = is important

This is called predicative use of the adjective.

Compare:

• Die oefening is belangrik. = The exercise is important.
• ’n belangrike oefening = an important exercise.

So when the adjective comes before a noun, it often takes -e:

• belangrike oefening

But after is, it stays:

• is belangrik

Yes, often you can.

For example:

• Beide die opwarming en die afkoeloefening is belangrik.

This also means Both the warm-up and the cool-down exercise are important.

Very roughly:

• sowel ... as ... = both ... as well as ...
• beide ... en ... = both ... and ...

Both are natural, though sowel ... as ... is a very common textbook-style structure to learn.

Not especially. The structure is:

• Sowel X as Y = subject
• is = verb
• belangrik = complement/adjective

So the sentence pattern is basically:

• [Both X and Y] + is + important

Afrikaans main-clause word order still puts the conjugated verb in the usual second position:

• Sowel die opwarming as die afkoeloefening is belangrik.

The whole sowel ... as ... phrase functions together as the subject.

A rough English-friendly guide would be:

• Sowel ≈ soh-vell
• die ≈ dee
• opwarming ≈ op-var-ming
• as ≈ ahs
• die ≈ dee
• afkoeloefening ≈ af-kool-oo-fuh-ning
• is ≈ iss
• belangrik ≈ buh-LUNG-rik

A few helpful notes:

• Afrikaans w sounds like English v
• g in belangrik is not a hard English g; it is a throat sound
• oe sounds like oo in food

This is only an approximation, but it can help you get started.

Yes. In Afrikaans, die is often used where English might or might not use the, depending on style and context.

Here, die opwarming and die afkoeloefening refer to specific activity types in a general but identifiable way, so die is natural.

Afrikaans often uses the definite article in places where English learners may not expect it, so it is worth getting used to the pattern rather than translating word-for-word.

Not necessarily. Afrikaans may express this idea in different ways depending on context, for example with wording based on afkoel (cool down) or a phrase that describes cooling down after exercise.

But in this sentence, afkoeloefening is a straightforward compound noun meaning a cool-down exercise, and it is easy to understand because Afrikaans likes compound words.

A very useful pattern is:

• Sowel die X as die Y is belangrik.
• Both the X and the Y are important.

You can reuse it with other nouns, for example:

• Sowel die dieet as die oefening is belangrik.
  Both the diet and the exercise are important.

• Sowel die onderwyser as die student is gereed.
  Both the teacher and the student are ready.

This makes the sentence a very useful model for building your own Afrikaans sentences.