I still don't understand why I need to use init. Using x twice in the video confused me.

More information on initialisers can be found in the official documentation here

Which provides the following description,

Initialization is the process of preparing an instance of a class, structure, or enumeration for use. This process involves setting an initial value for each stored property on that instance and performing any other setup or initialization that is required before the new instance is ready for use.

In the following example you will see that while we have declared that temperature is a double, we provide the init method which has an initial value. You could however have temperature = temperature within the init() which would in turn expect an input when Fahrenheit is called.

struct Fahrenheit {
    var temperature: Double

    init() {
        temperature = 32.0
    }
}
var f = Fahrenheit()
print("The default temperature is \(f.temperature)° Fahrenheit")
// Prints "The default temperature is 32.0° Fahrenheit"

This is my understanding, if anyone else has corrections or additions please post them.