Yea this is just syntax, every language does it a little different, most popular languages seem to derive off of C in some capacity. Some do it more different than others, and some are unholy conglomerations of unrelated languages that somehow works. Instead of saying why is this different, just ask how does this work. It's made my life a lot simpler.

var test int is just int test in another language.

func (u User) hi () { ... } is just class User { void hi() { ... } } in another language (you can guess which language I'm referencing I bet).

map := map[string]int {} is just Map<String, Integer> map = new HashMap<>() in another (yes it's java).

Also RTFM, this is all explained, just different!

Edit: I also know this is a very reductive view of things and there are larger differences, I was mostly approaching this from a newer developers understanding of things and just "getting it to work".