Translation:I am an apple.
My favorite joke is involves a shapeshifting doctor who turns into an apple (children thought he was really cool until he got really annoying showing off all the time, so without letting on that they were tired of him, they convinced him to turn into an apple), so naturally that's what I thought of when I saw this.
The children put the doctor who is an apple into a container, but the container is opaque, and they don't want to open it to risk letting the doctor out, but they also want to make sure that he's still in there, so they weigh the container every day to make sure it weighs the same.
Because, as we all know, a weigh a day keeps the doctor an apple.
You will encounter -이에요 later on. You will use 예요 when there is no batchim (the consonant at the bottom of the word, e.g. the ㄴ in 연준) as in 범규예요 (it is Beomgyu) and use 이에요 when there is batchim as in 수빈이에요 (it is Soobin)
Correct me if I'm wrong, i got my info from the Talk To Me in Korean app.
It's known as speech level, and the difference is the formality.
-이예요 is the casual speech level, which you would use to people like shop owners, delivery people, taxi drivers, and it's your best bet if you don't know the appropriate speech level for the situation
-입니다 is the formal speech level, which you would use for things like job interviews, court and political proceedings, etc.
There are two other speech levels (intimate and neutral) that will be covered later in the course, and three additional ones that are not covered in the course since they are rarely used in modern Korean.
I believe many Greeks in the '80s have watched "Frutopia", a television programme for kids (and older people), where the mayor of Frutopia was Emilios the apple (Αιμίλιος το μήλο). Frutopia was a town with all kinds of fruits (e.g. Maroulita (the lettuce), Thanos (the zucchini), Mata (the tomato) etc. So, this sentence makes sense for me.