Hai teman! This is because the English pronoun can be translated to different Indonesian pronouns, depending on the context.

"Kamu" can be informal, intimate (used by lovers), polite, familiar, less formal (depending on the cultural background)

"Anda" (always written in capital letter) can be formal, polite, very formal (sometimes impolite when addressing aged people), sometimes old-fashioned in colloquial speech, proper in official or public announcements, can be weird or ironical when addressing a little child

"Kalian" (plural) can be informal, familiar, polite

"Anda sekalian" plural version of "Anda"

When addressing people, there are other polite forms, as "Pak" ("Bapak") for males, "Bu" ("Ibu") for females, and also using the proper nouns or surnames.

Selamat belajar! :)