Sy lees die helfte van die oogkaart.

A simple breakdown is:

• Sy = she
• lees = reads / is reading
• die helfte = half / the half
• van = of
• die oogkaart = the eye chart

So the structure is basically She reads half of the eye chart.

Yes, sy can mean two different things depending on how it is used:

• sy before a verb = she
• sy before a noun = his

So:

• Sy lees = She reads
• sy boek = his book

In your sentence, sy is followed by the verb lees, so it must mean she.

Afrikaans verbs usually do not change according to the subject in the present tense.

So you get:

• Ek lees = I read
• Jy lees = you read
• Sy lees = she reads
• Ons lees = we read

Unlike English, there is no special -s ending for she.

It can mean either, depending on context.

Afrikaans often uses the simple present where English might use either:

• she reads
• she is reading

If you want to make the ongoing action extra clear, Afrikaans can say:

• Sy is besig om die helfte van die oogkaart te lees

But the shorter Sy lees ... is very normal.

This is a very common Afrikaans pattern:

die helfte van + noun

It means half of the noun.

So:

• die helfte van die koek = half of the cake
• die helfte van die boek = half of the book
• die helfte van die oogkaart = half of the eye chart

The word van is doing the job of English of.

Because there are two noun phrases that are definite:

• die helfte = the half
• die oogkaart = the eye chart

Afrikaans uses die as the definite article for basically all nouns, whether singular or plural, and regardless of gender.

So both parts take die.

Sometimes yes. You may hear half van die oogkaart in natural speech.

But die helfte van die oogkaart is a very standard and clear structure, especially for learners. It is the safest pattern to remember for half of ....

Because Afrikaans usually writes compound nouns as one word.

Here:

• oog = eye
• kaart = card / chart

Together they form:

• oogkaart = eye chart

This is very typical in Afrikaans and also in Dutch and German. The last part is the main noun, and the first part describes it.

It is the normal Afrikaans main-clause word order:

Subject + Verb + Object

So:

• Sy = subject
• lees = verb
• die helfte van die oogkaart = object

Nothing unusual is happening with the word order here.

A very rough English-friendly guide is:

say lease dee HELF-tuh fun dee OAKh-kaart

A few notes:

• sy sounds roughly like say
• lees is roughly like lease
• die is roughly dee
• helfte has the helf part clearly pronounced
• the g sound in oogkaart is the Afrikaans guttural sound, so it does not sound like a normal English g

That guide is only approximate, but it is enough to get you started.