Learn Hardcore Czech: Moje sestra studuje češtinu pravidelně každý večer. - My sister studies Czech regularly every evening.

Má is an older/shorter feminine form and sounds a bit more formal or literary: má sestra. In everyday modern Czech, moje sestra is more common and neutral.

Why is it sestra and not sestru or something else?

Sestra is in the nominative singular case, because it is the subject of the sentence – the person who is doing the action.

Kdo studuje? (Who is studying?) → Moje sestra.

If we changed the role in the sentence, the form would change, for example:

Vidím sestru. (I see my sister.) – accusative
Jdu se sestrou. (I am going with my sister.) – instrumental

In this sentence, she is just the doer, so the nominative sestra is correct.

Why is it češtinu and not čeština?

Češtinu is the accusative singular form of čeština (Czech language), used for a direct object.

The verb studovat (to study) normally takes a direct object in the accusative:

studuje češtinu (she studies Czech)
studuji matematiku (I study mathematics)
studujeme angličtinu (we study English)

For feminine nouns ending in -a, the accusative singular ending is usually -u:

čeština → češtinu
kniha → knihu
škola → školu

Is studuje češtinu the normal way to say “she studies Czech”? How is it different from učí se česky?

Both are correct, but they feel slightly different:

studuje češtinu
- more formal or academic
- suggests studying as a school subject, in a course, maybe systematically
učí se česky (literally: she is learning Czech / she is teaching herself in Czech)
- more general and everyday
- does not need to be in a formal course; could be apps, talking to people, etc.

In many contexts you could use either, but if you mean a formal course or school subject, studuje češtinu fits very well.

What tense is studuje? Does it mean “she studies” or “she is studying”?

Studuje is present tense, 3rd person singular, imperfective.

In Czech, the present tense usually covers both English she studies (habitual) and she is studying (right now). The time meaning comes from context or extra words:

Moje sestra studuje češtinu pravidelně každý večer.
→ a repeated, habitual action (like English she studies)
Teď moje sestra studuje češtinu v pokoji.
→ happening now (like English she is studying)

How does studuje agree with moje sestra?

The verb is conjugated for 3rd person singular because the subject moje sestra is one person (she).

The present tense of studovat is:

(já) studuju / studuji – I study
(ty) studuješ – you (sg) study
(on/ona/ono) studuje – he/she/it studies
(my) studujeme – we study
(vy) studujete – you (pl/formal) study
(oni/ony/ona) studují / studujou – they study

Moje sestra → ona → studuje.

Why is there no subject pronoun like ona? In English we say “She studies…”.

Czech normally drops personal subject pronouns when the verb ending already shows the person and number.

(Ona) studuje češtinu.
Both are grammatically correct, but just Studuje češtinu. is natural and standard.

You usually add ona only for contrast or emphasis:

Ona studuje češtinu, ale já studuji španělštinu.
(She studies Czech, but I study Spanish.)

Can I leave out moje and just say Sestra studuje češtinu pravidelně každý večer?

Yes, you can say:

Sestra studuje češtinu pravidelně každý večer.

In many real situations, context already makes it clear that you mean my sister, so moje is not always needed. However:

With moje sestra, you clearly specify that it is my sister (not someone else’s).
Without moje, it could mean the sister (sister in general, or a previously mentioned sister).

In an isolated sentence like this, Moje sestra… is clearer for a learner.

What do pravidelně and každý večer each add to the meaning? Is it redundant?

každý večer = every evening → tells you when and how often
pravidelně = regularly → tells you how she does it (in a regular, systematic way)

Together:

pravidelně každý večer suggests a very consistent habit: she follows a routine every evening.

You could say just one of them:

Moje sestra studuje češtinu každý večer. – every evening, but not stressing regularity as strongly
Moje sestra studuje češtinu pravidelně. – regularly, but the exact schedule is not specified

Using both is not wrong; it is a bit emphatic but natural in speech.

Can the word order of pravidelně and každý večer change? For example, can I say každý večer pravidelně?

Yes, Czech word order is quite flexible. These are all grammatically correct:

Moje sestra studuje češtinu pravidelně každý večer.
Moje sestra studuje češtinu každý večer pravidelně.
Moje sestra každý večer pravidelně studuje češtinu.
Každý večer moje sestra pravidelně studuje češtinu.

The basic meaning stays the same. Different orders can slightly change the rhythm or emphasis, but as a learner you can treat them as equivalent. The version you gave is a perfectly natural, neutral order.

Why is it pravidelně and not pravidelný?

Pravidelně is an adverb (how? in what manner?) → regularly.
Pravidelný is an adjective (what kind of?).

You need the adverb because it describes the verb:

Studuje pravidelně. (She studies regularly.)

The adjective pravidelný would describe a noun:

pravidelný student (a regular student)
pravidelné učení (regular studying – as a noun phrase)

How do you pronounce češtinu and what do the little marks (č, š, ť, ň) mean?

Češtinu is pronounced roughly: [chesh-tee-noo].

Letter by letter:

č = like English ch in church, but a bit sharper
e = like e in bed
š = like sh in she
ti (here) = [ťi], a softened t
- i (similar to ty in British, but softer and palatal)
nu = noo

The small hooks (háček) above consonants show palatalized or “soft” sounds:

č, š, ž – ch, sh, zh
ď, ť, ň – very soft d, t, n pronounced with the tongue closer to the palate

In češtinu, the stress is always on the first syllable: ČE-šti-nu.