I wonder what "a get-acquainted day" means.
Hello
The first day of school is a get-acquainted day.
Get-acquainted literally means get to know each other.
Is it close to orientation?

Yes it is essentially an orientation day but using that term puts emphasis on the day being about getting to know your environment or practical matters.
I'm guessing they've used "get-acquainted day" to make it sound more fun and put the focus on getting to know your fellow classmates instead.