Sy eet, waarna sy slaap.

Here, sy means she.

A useful extra note: in Afrikaans, sy can also mean his in other contexts, so learners sometimes get confused. In Sy eet, waarna sy slaap, both instances are the subject pronoun she.

No. Afrikaans verbs usually do not change according to the subject the way English verbs do.

So:

• ek eet = I eat
• jy eet = you eat
• sy eet = she eats
• ons eet = we eat

That is why you get sy eet, not a special form like English she eats.

Waarna means something like after which or after that.

In this sentence, it links the first action to the next one:

• Sy eet = she eats
• waarna sy slaap = after which / after that she sleeps

It is a more linked, formal-sounding connector than simply saying then.

It is historically made from:

• waar = where / which / what (in relative-type forms)
• na = after

So waarna literally has the sense of after which.

You do not need to translate it word-for-word every time, but knowing this helps you understand why it connects back to the previous clause.

Because waarna sy slaap is a subordinate clause linked to the first clause.

Afrikaans normally uses a comma to separate a main clause from a subordinate clause like this:

• Sy eet, waarna sy slaap.

That comma is standard and expected here.

Because waarna introduces a subordinate clause.

In Afrikaans subordinate clauses, the verb typically comes later in the clause, often at the end. In this short example, there are only two elements after waarna:

• sy = subject
• slaap = verb

So you get:

• waarna sy slaap

Compare this with a main clause:

• Daarna slaap sy. = After that, she sleeps.

So waarna sy slaap follows subordinate-clause word order, while daarna slaap sy is a main-clause pattern.

Because the second part is its own clause and needs its own subject.

English does the same in a sentence like:

• She eats, after which she sleeps.

You cannot normally just say Sy eet, waarna slaap because slaap still needs a subject.

It is grammatical, but it sounds a bit formal or written.

In everyday Afrikaans, people would often say something simpler, such as:

• Sy eet en daarna slaap sy.
• Sy eet en dan slaap sy.

So waarna is perfectly correct, but it has a slightly more formal, narrative, or written style.

Good question.

• waarna = after which / after that, and it links back to the previous clause in a more formal way
• daarna = afterwards / after that / then, often used more simply in everyday speech

Compare:

• Sy eet, waarna sy slaap.
  More formal, more tightly linked.

• Sy eet. Daarna slaap sy.
  Very natural and straightforward.

Both can express the same basic sequence, but the style is different.

Yes, but the structure changes.

Nadat means after and introduces a subordinate clause more directly:

• Nadat sy geëet het, slaap sy.
  = After she has eaten, she sleeps.

That is different from:

• Sy eet, waarna sy slaap.

So nadat and waarna are related in meaning, but they are not swapped in without changing the sentence structure.

It is in the present tense.

In Afrikaans, the present tense can describe:

• a habitual action: she eats and then sleeps
• a general sequence
• a narrative present

So without more context, Sy eet, waarna sy slaap can mean a regular pattern or simply describe events in a present-style narrative.

A rough English-friendly guide would be:

• Sy ≈ say but with a diphthong closer to Dutch/Afrikaans ei
• eet ≈ eat
• waarna ≈ VAAR-nah
• slaap ≈ slahp

So roughly:

Say eet, VAAR-nah say slahp

This is only an approximation, but it is enough to get started.