Why do i need to pass in two arguments in the init method when that was already being done earlier?

When you have custom initialisers in Struct's they take arguments. Say you had an arguments firstName & lastName and you have two constants in the struct firstName and lastName.

struct Names{
  let firstName : String
  let lastName : String
  var age : Int?
  init(firstName: String, lastName: String)
  {
    //firstName = firstName Wouldn't work as the compiler would think you are talking about firstName within scope
    self.firstName = firstName //Indicates you want to access a variable outside scope and assign it the one from within
    self.lastName = lastName
  }
}

Whenever you create an instance of the struct you need to pass it the values that you specify in the custom initialiser. A struct is different to a class which you will learn further down the course, but the idea is when you initialise it you will assign it to a variable and then do you're work from there. eg:

var names = Names(firstName: "John",lastName: "Doe")
names.age = 28
println("\(names.firstName) \(names.lastName) is \(names.age!)")

As you can see from that block, since we init'd the struct and assigned it to 'names' we can then manipulate the optional variables within the struct or access any other methods within it.

Hope this helps.