Ek kyk deur die venster.

Afrikaans usually does not use a separate verb like English am in this kind of present-tense sentence.
Ek kyk can mean both:

• I look
• I am looking

The exact meaning comes from context. So Afrikaans present tense is often broader than English present tense.

Afrikaans verbs normally do not change form for different subjects in the present tense.

So you get:

• Ek kyk = I look
• Jy kyk = you look
• Hy kyk = he looks
• Ons kyk = we look

Unlike English, there is no special -s form like he looks.

Because deur is already the preposition you need here.

Compare:

• Ek kyk na die venster = I look at the window
• Ek kyk deur die venster = I look through the window

With kyk, you often use na when you are looking at something. But if you want another relationship, such as through, into, or over, you use the appropriate preposition instead.

Yes. Deur can be:

• a preposition meaning through
• a noun meaning door

In this sentence, it is clearly the preposition through because it comes before die venster and forms the phrase deur die venster.

So context tells you which meaning is intended.

Die is the normal definite article in Afrikaans, meaning the.

A useful thing for English speakers to know is that Afrikaans uses die for:

• singular nouns
• plural nouns
• all genders

So Afrikaans does not change the word the way German does, and it does not have separate forms like the for masculine/feminine/neuter.

Sometimes, yes. In some contexts die can also function like that/those, depending on stress and structure.

But in Ek kyk deur die venster, it is just the ordinary article the:

• die venster = the window

Yes, in this simple main clause it is very similar:

• Ek = subject
• kyk = verb
• deur die venster = prepositional phrase

So the pattern is:

subject + verb + prepositional phrase

That said, Afrikaans is a verb-second language. In a basic sentence like this, the subject comes first, so the verb also appears early. But if you move something else to the front, the verb still stays in second position:

• Deur die venster kyk ek.

That version is possible, but less neutral than Ek kyk deur die venster.

It can mean both, depending on context.

For example:

• Ek kyk deur die venster = I look through the window
• Ek kyk televisie = I watch television

So kyk is a broad verb. In your sentence, because of deur die venster, the meaning is clearly look rather than watch.

The difference is important:

• Ek kyk deur die venster = I look through the window
• Ek kyk na die venster = I look at the window

So:

• deur focuses on seeing through the glass/opening
• na focuses on the window itself as the thing you are looking at

A rough guide:

• ek ≈ eck
• kyk has no exact English equivalent, but it sounds roughly like kake said very quickly, ending clearly in k
• deur also has no exact English equivalent; it is somewhat like dare but with a more rounded vowel
• venster ≈ VEN-ster, with the stress on the first syllable

The safest approach is to hear native audio, because the vowels in kyk and deur are not exact matches for standard English sounds.

A common Afrikaans way to make the action feel more explicitly ongoing is:

Ek is besig om deur die venster te kyk.

Literally, this is something like I am busy looking through the window, but in normal use it often just means I am looking through the window right now.

So:

• Ek kyk deur die venster = neutral present; can mean I look or I am looking
• Ek is besig om deur die venster te kyk = more clearly I am looking right now