Er studiert Physik.

Because the subject is er (he), which is third-person singular. In the present tense, the verb studieren changes depending on the subject:

• ich studiere
• du studierst
• er/sie/es studiert
• wir studieren
• ihr studiert
• sie/Sie studieren

So with er, the correct form is studiert.

In German, studieren usually means to study a subject at a university or college. So Er studiert Physik normally suggests that he is a university student studying physics as his academic subject.

This is a little narrower than English study, which can also mean general learning. For example:

• Er studiert Physik. = He studies physics / He is a physics student.
• Er lernt Physik. = He is learning physics.

In many contexts, studieren sounds more formal and academic than lernen.

Because Physik is a noun, and all nouns in German are capitalized.

This is one of the most noticeable spelling rules in German. So you get:

• die Physik
• das Buch
• der Student

Even when a noun is not at the beginning of the sentence, it still gets a capital letter.

Because school subjects and academic subjects are often used without an article when talking about what someone studies, learns, teaches, or likes as a subject.

So German commonly says:

• Er studiert Physik.
• Sie studiert Mathematik.
• Ich mag Geschichte.

You can use an article in other contexts, but in this sentence it would sound unnatural. The bare noun is the normal choice.

Physik is in the accusative case, because it is the direct object of studiert.

In this sentence:

• Er = subject, so nominative
• studiert = verb
• Physik = direct object, so accusative

However, you do not see any visible change here, because Physik has no article in the sentence. If there were an article, the case would be easier to spot.

Yes. This is the normal German main clause word order:

• Subject + verb + object

So:

• Er = subject
• studiert = verb
• Physik = object

German is a verb-second language in main clauses, which means the finite verb usually comes in the second position. Here, Er is in the first position, so studiert must come second.

A yes/no question is formed by putting the verb first:

• Studiert er Physik? = Is he studying physics? / Does he study physics?

If you want a question word, that word comes first, and the verb still comes before the subject:

• Was studiert er? = What is he studying?
• Wo studiert er Physik? = Where does he study physics?

Yes, but it means something a little different.

• Er studiert Physik usually means he is studying physics as a university subject.
• Er lernt Physik means he is learning physics, perhaps for school, an exam, or on his own.

So both can translate naturally into English, but the German verbs are not always interchangeable.

It is pronounced approximately shtoo-DEERT.

A few helpful points for English speakers:

• st at the beginning of a syllable in standard German often sounds like sht
• u is like oo in food
• the stress is on the second syllable: stu-DIERT

And Physik is approximately füh-ZEEK in standard German, with the stress on the second syllable.

Yes. The German present tense often covers both meanings that English separates into:

• He studies physics
• He is studying physics

German often uses the simple present where English might use either the simple present or the present continuous. The exact meaning depends on context.

Because er is the normal third-person singular masculine pronoun, meaning he. Just like in English, German often uses a pronoun once the person is already known from the context.

For example:

• Tom ist Student. Er studiert Physik.

After mentioning Tom, German naturally uses er to refer back to him.