Az optikus lencsét választ.

Hungarian has two forms of the definite article:

• a before a consonant sound
• az before a vowel sound

Because optikus starts with the vowel o, the correct form is az:

• az optikus

This is similar to English a/an, but Hungarian uses this distinction only for the definite article.

Because lencsét is the accusative form, and the accusative marks the direct object of the verb.

Here, the thing being chosen is the lens, so lencse needs object marking:

• lencse = lens
• lencsét = lens, as the direct object

In Hungarian, the accusative is usually marked with -t.

This is a regular spelling and sound change in Hungarian.

Nouns ending in -a or -e usually change that final vowel to á or é before certain suffixes, including the accusative -t:

• alma → almát
• zene → zenét
• lencse → lencsét

So lencsét is the expected form.

Hungarian often shows this through case endings, not mainly through word order.

• optikus has no special ending here, so it is the subject
• lencsét has the accusative ending -t, so it is the object

So even if the word order changes, lencsét is still clearly the thing being chosen.

This is about Hungarian’s indefinite and definite verb conjugation.

• választ = indefinite conjugation
• választja = definite conjugation

Hungarian usually uses the definite conjugation when the object is definite and specific, for example:

• A lencsét választja. = He/she is choosing the lens.

In your sentence, lencsét has no definite article, so it is treated as indefinite, and the verb stays in the indefinite form:

• Az optikus lencsét választ.

Hungarian often leaves an indefinite object without an article, especially in simple, natural verb-object expressions.

So:

• lencsét választ = chooses a lens / is choosing lens(es) in a general sense

You could also say:

• egy lencsét választ

That would make the one / a idea more explicit. Without egy, the sentence sounds a bit more general or less specifically individuated, but English will still usually translate it as a lens.

No, Hungarian word order is flexible, but changing it often changes the emphasis.

Az optikus lencsét választ is a natural sentence with the object before the verb.

Other orders are possible, but they may sound marked or emphasize something different. For example:

• Lencsét választ az optikus.
  This can put more focus on lencsét.

• Az optikus választ lencsét.
  This is possible in some contexts, but it is not the most neutral version here.

So the given order is a good basic pattern to learn.

The dictionary form is választani, which means to choose / to select.

From that infinitive:

• választani = to choose
• választ = he/she chooses, or it can also mean chooses with an explicit subject like az optikus

So in this sentence, választ is the third person singular present tense form.

A few useful pronunciation points:

• Az sounds roughly like awz.
• optikus starts with stress on the first syllable: OP-ti-kush
• sz is pronounced like English s
• cs is pronounced like English ch
• é is a long vowel, roughly like ay in a careful pronunciation
• választ has sz = s, so it sounds roughly like VAA-lasst

Very approximate pronunciation of the whole sentence:

• Az OP-ti-kush LEN-chayt VAA-last

Also remember: in Hungarian, the stress is normally on the first syllable of each word.

No. Hungarian profession words usually do not show gender.

So optikus can mean:

• a male optician
• a female optician

The sentence itself does not tell you which one it is. You would only know from context or from extra words added elsewhere.