What's the difference between GOOD and WELL?
GOOD is an adjective and WELL is an adverb.
We eat well, (as we are describing how we eat and drink.)
Adverbs answer the question HOW, and adjectives answer the question What sort of ...
She speaks good Japanese.
She speaks Japanese well.
She speaks Japanese better than I do.
Note that better is the comparative form of both good and well.
There are some exceptions:
When we use verbs such as be, seem, appear, sound, look, feel, smell, taste, they are followed by adjectives rather than adverbs as we are describing the subject of the sentence rather than the action of the verb.
She looks really good in those clothes.
The food at the reception tasted really good - better than the food we had last year.
There's no way he'll get a distinction, but the work he's done appears good enough for a pass.
I felt really good when she congratulated me on winning the essay prize.
For similar reasons we would talk about:
A good-looking woman.
A good-natured boy. (good describes his nature).
But we would also say:
A well-dressed woman. (WELL tells us how she dresses)
A well-behaved boy. (WELL tells us how he behaves)
The only time when WELL can be used as an adjective by itself is when we are talking about someone's health. Here well means in good health.
How are you today? Fine. Very well, thanks. / Not very well, actually.
I often feel unwell when I'm on a boat, but as soon as I get off, I'm fine.
Note that the expression well and good is used to indicate that you find a particular situation satisfactory or acceptable.
If you can do the job in less time and leave early, I don't mind. That's (all very) well and good.
If you want to stay here on your own over Christmas, well and good.
Incidentally, there is now a trend among young people, particularly in the 18 - 25 age range, to use WELL instead of VERY in informal expressions like:
I am well happy with that.
I was well tired last night.
She was well pleased with her birthday present.
Again it breaks the rule and is effective in the impact it makes.