You are writing a book on romance, and you remembered how you fell in love with your fiance or spouse. The way you present such feeling or attitude is refer to as tone.
Tone is your attitude towards your writing to your audience. Your writing reflect your emotions.
One of the essences of tone is to consider who you are writing to. Understand that the message you are writing to your boss, is not the one you are writing to your friend. The way you write to a married person, is not the way you are expected to write to a teenager.
What then is mood? Have you ever read a book, and you felt like crying? Probably you have John Donne’s poem DEATH BE NOT PROUD? What was your feeling? What you felt, is your mood. Not everybody can have a particular mood towards a literary work.