gut
good
Describes high quality, correct execution, or a positive characteristic.
Das ist ein wirklich gutes Buch.
That is a really good book.

good
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good
Describes high quality, correct execution, or a positive characteristic.
Das ist ein wirklich gutes Buch.
That is a really good book.

When 'gut' (good) is an adjective that describes a noun, it is declined. When it is an adverb that describes a verb, it always remains unchanged in the form 'gut' (well).
Er hat mir einen guten Rat gegeben.
He gave me a good piece of advice.
To talk about well-being, the fixed expression 'es geht jemandem gut' (someone is doing well) is used. The person being talked about is always in the dative.
Wie geht es deinen Eltern?
How are your parents?
In combination with an expression of time or measurement, 'gut' (a good) means something like 'at least' or 'a little more than'. It expresses a generously measured amount.
Die Fahrt zum Flughafen dauert eine gute halbe Stunde.
The drive to the airport takes a good half hour.
The expression 'Ist ja gut' is used colloquially to end a discussion or calm someone down. Here it means 'enough' or 'all right'.
Ist ja gut, ich habe verstanden und werde es tun.
All right, that's enough, I understand and will do it.
In the meaning of 'high quality', 'gut' (good) is often combined with nouns such as 'Arbeit' (work), 'Idee' (idea), 'Qualität' (quality), or 'Ergebnis' (result).
Das war eine wirklich gute Idee von dir.
That was a really good idea of yours.
As an adverb, 'gut' (well) often describes activities such as 'schlafen' (to sleep), 'verstehen' (to understand), 'kennen' (to know), or 'funktionieren' (to work/function).
Ich habe letzte Nacht nicht gut geschlafen.
I didn't sleep well last night.
When 'gut' means 'fitting' or 'suitable', it often appears with words such as 'Gelegenheit' (opportunity), 'Moment' (moment), 'Zeitpunkt' (point in time), or 'Preis' (price).
Das ist eine gute Gelegenheit, um Fragen zu stellen.
This is a good opportunity to ask questions.
probably / well
'gut' and 'wohl' can both have to do with well-being. You can say: 'Ich fühle mich gut' (I feel good / well) or 'Ich fühle mich wohl' (I feel well / comfortable). 'gut' is more general and can also describe quality or doing something well. 'wohl' fits especially with a pleasant physical or emotional feeling, often in the phrase 'sich wohl fühlen' (to feel well / comfortable). Learners may confuse the words because both can fit when talking about health or feelings. Important: 'wohl' on its own can also mean 'probably', for example 'Er kommt wohl später' (He will probably come later). That is not the same as 'gut'.

Nach der Pause kann sich meine Freundin wieder gut konzentrieren.
After the break, my friend can concentrate well again.
Nach dem Essen fühlt sich meine Freundin wieder wohl.
After the meal, my friend feels well again.