Is "be up to" an expression? What does it mean?

Is there a big difference in meaning between "talk to" and "talk with"?

In general, "talk to" can mean that one person is talking and the other is mostly listening. it can be used for one way conversations. "talk with" is used for two way communications. Ex: I talked to him about his low scores. Ex: he is a weird guy. he talks to animals. Ex: I talked with my friend about our trip.

What's "homecoming"?

"Homecoming" is an American high school and college tradition. It's when many of the school's alumni and current students come back to watch a football game. The week following up to the big game, there are dress-up days at school, a school dance, a parade, etc. There is also a vote from the students on a Homecoming King and Queen in their senior (last) year of school.

I think I've heard the word "junk" more in American media. Then, does the word "rubbish" is rather closer to British English?

Yes, that's right! "Rubbish" is considered British English. However, I'd say American English uses "trash" as an alternative to "rubbish". The word "junk" is used in American and British English when referring to unwanted items. Ex: There's so much junk in your room. You need to throw it out! Ex: Honey, did you take the trash out? => American English Ex: Honey, did you take the rubbish out? => British English

What does "animal control" mean?

"Animal control" is a noun that means the office or governmental department in charge of taking control of animals in specific situations, such as dangerous animals, animals that are lost or are strays, and abused animals. They're also in charge of finding homes for animals or returning them to their homes. Ex: The dog seemed dangerous, so we called animal control. Ex: There were a few stray cats on this street, but I think animal control took them.

Why did he use "where" here? Could you give me some more similar examples?

People sometimes use "when" and "where" fairly interchangeably and this is the case here. "Where" is being used to mean a place in time, rather than an actual location. Ex: We're living in a time where, more than ever, everyone has a voice. Ex: He found himself in a situation where he had to make a hard decision. Ex: I've been in a situation where I was terrified.