Ruby: What is "Self" inside "If" Statement of Instance Method

What does "self" refer to when it's inside an "if" statement (or is it called block?) that is inside an instance method?

I'm referring to my code in the last method: "apply_discount"

I thought it'd get me the @total and @discount instance variables, but it's not doing so.

So, basically, how would I get these variables from the my place in the "if" statement I'm referring to by using "self"?

Or should I use another way?

class CashRegister

    attr_accessor :total, :discount

    def initialize(discount = 0)
        @total = 0
        @discount = discount
    end

    def add_item(title, price, quantity = 0)
        if quantity > 0
            self.total += (price * quantity)
        else
            self.total += price
        end
    end

    def apply_discount
        # total = self.total
        # discount = self.discount
        if self.discount > 0
            self.total = self.total - (self.total * (self.discount / 100.0))
            "After the discount, the total comes to $#{self.total}."
        else
            "There is no discount to apply."
        end
    end
end

Thanks for your help!