Tone
I don't know about you, but I can easily write a descriptive scene of a mom growing more and more angry with her kid. I would describe the mom with her arms crossed and her mouth in a firm line. She'd tap her foot with impatience and yell to her kid, 'Get downstairs. Right. Now.'
Tone is the author's overall attitude toward a subject. In my scene, my attitude toward the mom character reflects her anger and impatience with her child. In literature, tone is conveyed through the author's use of language, including word choice, phrasing and sentence structures. Tone is in the details that are included or omitted in the text.
Notice that I chose to describe the mom with crossed arms and a mouth in a firm line, to show she is angry. We might learn later that the mom character has beautiful brown eyes, but including that detail in this scene wouldn't have served my purpose in showing her frustration.
Mood
Tone and mood are often confused, so now would be a good time to make sure you understand the difference between the two.
If tone is the author's attitude toward a subject, then mood is how we are made to feel as readers, or the emotion evoked by the author. So, while it's clear from my portrayal that the subject, a mom, is angry (tone), the reader might feel I'm describing a familiar scene and maybe chuckle in recognition (mood).
Both tone and mood are implied by the author's use of words, so it's easy to see how they come to be used interchangeably. Charles Dickens doesn't come out and say that the tone of the book Great Expectations is X and the mood is Y, nor does his attitude toward Pip and his changing fortunes stay the same through the entire 490 page novel.
Let's look at an early passage, when a very young Pip goes to visit his parents' graves:
'My first most vivid and broad impression of the identity of things, seems to me to have been gained on a memorable raw afternoon towards evening. At such a time I found out for certain, that this bleak place overgrown with nettles was the churchyard; and that Philip Pirrip, late of this parish, and also Georgiana wife of the above, were dead and buried...and that the dark flat wilderness beyond the churchyard...was the marshes; and that the low leaden line beyond, was the river; and that the distant savage lair from which the wind was rushing, was the sea; and that the small bundle of shivers growing afraid of it all and beginning to cry, was Pip.
'Hold your noise!' cried a terrible voice...'Keep still you little devil, or I'll cut your throat!'
The setting is characterized as dangerous and threatening - 'bleak place overgrown with nettles', 'dark flat wilderness', 'low leaden line', 'distant savage lair'- and the characters are terrified or terrifying - 'small bundle of shivers', 'a terrible voice.'
This first scene, with its emotion-evoking setting, characters and language, makes me think this author has a fairly bleak attitude toward the marshes where Pip grows up. The tone says this is not a nice place nor a happy childhood memory.
Dig a little deeper, though, and you'll get the mood. First, the descriptive and precise language creates a vivid picture, including 'the small bundle of shivers growing afraid of it all and beginning to cry'. The tone might be bleak, but the mood is thrilling and just a bit scary. It makes me want to know what next happens to this kid.