The := operator is called walrus operator and is inspired by Python I think. It's declaring a variable and assigning it in one go. map[string] int is defining a map (associative array or also known as dictionary in Python), with string as key type and int as value type. And the following {} is the body of the associative array, meaning empty content.

I only played a bit with Go and did basic tutorials. I might go back to it at some point, but Zig is much more appealing to me. Go is too simple in the language to me, but on the other side, this is exactly whats appealing.