Is 제 친구의 집에서 내일 놀아요 considered correct or wrong?
It is correct.
What part of the sentence makes it mean "Let's hang out?" I thought such a construct would require a -ㅂ 시다 rather than "어요".
Duolingo tips and notes on website say it can be either.
What does 놀아요 mean..? I thought it meant "to play"
It's something said in some Asian languages. Literally "play"
Why 집에서? And in “Let’s hide in this school” 학교에 is used instead of 학교에서 ?
I got the same question
Does the time (i.e. tomorrow, today, yesterday) always have to be placed at the beginning of the phrase?
Technically, no, but that is what is most commonly done.
It's usually placed before the location. In English it's usually the opposite
Warum ist es falsch 내일 제 친구의 집에서 만나요 zu sagen?
Es tut uns leid, ich kann kein Deutsch. Ich glaube ich weiß was du fragst.
만나요 = "treffen"
놀아요 = "heraushängen"
Entschuldigung, wenn ich Fehler gemacht habe!
Dein Deutsch ist echt super! Wir würden eher "abhängen" als "heraushängen" sagen, aber ansonsten perfekt!