A method expression is a function that can be called like a regular function, except that you also pass the object to act on as the first argument. This is because it needs to know which object to use.
Normally, you would just use the following:
d := &Dog{}
d.Bark(5)
But using a method expression, you can "save" the function, allowing you to pass it to something else. For example, you could choose to use (*Dog).Bark
or (*Dog).Sit
as an action, and call it from a helper. eg:
func main() {
var b func(*Dog, int)
if (shouldBark) {
b = (*Dog).Bark
} else {
b = (*Dog).Sit
}
d := Dog{}
DoAction(b, &d, 3)
}
func DoAction(f func(*Dog, int), d *Dog, n int) {
f(d, n)
}
The specific syntax (*Dog).Bark
means that you are deriving a function for a method with pointer receiver.
Honestly, these are not very frequently used. I would recommend you get a good grasp of the language first (eg: take the entire Go tour), then explore less used functionality at a later date.