Go has a scheduler that lets you write synchronous code, and does context switching on its own and uses async I/O under the hood. So if you’re running several goroutines, they might run on a single system thread, and when your code is blocking from the goroutine’s view, it’s not really blocking. It’s not magic, but yes, it masks all this stuff from you.
The scheduler will allocate system threads when they’re needed, and during operations that are really blocking (file I/O is blocking, for example, or calling C code). But if you’re doing some simple http server, you can have thousands and thousands of goroutines using actually a handful of “real threads”.
You can read more about the inner workings of Go here.