Why and when should we use an initializer?

I'm a beginner as well, so someone correct me if i'm wrong.

the init() is a function/method. It is used to do things, when in your source code an instance of a class (or struct as well?) is created. Not sure how much you know about classes and creating instances of classes. If you don't, wait until you have that and you might understand. If yes: creating an instance of e.g. a class will call this method.

init() on a beginner level is mainly used to initialise the variables. You are not setting hard values here, but say "hey user, when you create on object of me (the class) I want you to initialise the parameters (means setting the values), that I have declared in my init-method". This "forces" the user to set values.

The assignment in init() is a bit confusing. The variable right to the = is a parameter. This parameter has to be set during creation of a class object. This is then assigned to the class' property, that is on the left of the = sign. You can e.g. write "self.x = x" or "xProperty = xParameter" or "x = _x". See the example below:

class Person {
   //Properties (synonyme for variables in a class)
   var name: String
   var age: Int

   init(inputName: String, inputAge: Int) {
      name = inputName
      age = inputAge
   }
}

Can we leave this out? Yes, init() is not required. BUT, then we 1. create a class instance that does not ask for parameters, which might be a problem when we want to set them and 2. we need to initialise the properties right at the moment of the declaration. So it needs to be 'var name: String = "initialName" ' instead of 'var name: String'.

I'm yet a newbie, but when creating a class, I for now always create the init-method, until I know better.