Learn Hardcore Arabic (Modern Standard): أنا طالب في هذه المدرسة.

In Arabic, the subject pronoun is often optional because the verb (in verbal sentences) usually shows who is doing the action. But this sentence is a nominal sentence (no verb written), so starting with أنا (I) is a common way to make the subject explicit.
You can often drop أنا if the context already makes it clear who you mean, but it can sound more complete or emphatic with it, especially for introductions.

Where is the verb to be (am/is/are)? How can the sentence mean “I am a student…” without am?

Modern Standard Arabic usually omits the present-tense “to be” in simple statements. So:

أنا طالب literally = I (a) student → “I am a student.”
The “am” is understood.

If you need “to be” in other tenses, Arabic uses كان and its forms (e.g., “I was…”), but in the present, it’s typically not written.

What is the grammatical structure of أنا طالب?

It’s a nominal sentence:

أنا = the subject (مبتدأ)
طالب = the predicate (خبر)

So it’s “Subject + description,” with the linking “am” implied.

Why is طالب indefinite (no ) even though English says “a student”? How do I show or in Arabic?