zufrieden
satisfied
Describing the state in which you are happy with a situation, performance, or result and do not want any change.
Der Kunde war mit dem Service sehr zufrieden.
The customer was very satisfied with the service.

satisfied
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satisfied
Describing the state in which you are happy with a situation, performance, or result and do not want any change.
Der Kunde war mit dem Service sehr zufrieden.
The customer was very satisfied with the service.

The word is made up of 'zu' and 'Frieden' (peace). So someone who is zufrieden (satisfied) is literally 'at peace' with a situation.
Nach einem langen Arbeitstag war er einfach nur zufrieden, zu Hause zu sein.
After a long workday, he was simply satisfied to be at home.
The adjective 'zufrieden' (satisfied) is almost always used with the preposition 'mit' (with) and the dative to express what you are satisfied with.
Ich bin mit meiner neuen Wohnung sehr zufrieden.
I am very satisfied with my new apartment.
'Zufrieden' (satisfied) can also be used as an adverb to describe a verb. It then expresses that an action is carried out in a satisfied state.
Er lehnte sich zufrieden zurück und schloss die Augen.
He leaned back contentedly and closed his eyes.
The expression 'jemanden zufrieden lassen' (to leave someone alone) means to leave a person in peace. The person who is to be left in peace is in the accusative.
Er wollte über das Thema nicht mehr reden, also ließ ich ihn zufrieden.
He didn't want to talk about the topic anymore, so I left him alone.
happy / lucky
'glücklich' and 'zufrieden' both describe a positive state. 'glücklich' refers more to joy and a warm, strong feeling. 'zufrieden' means that something is okay and you do not want it to change. It fits well with results, performance, work, or a situation. Learners confuse the words because satisfaction is often part of happiness. But 'zufrieden' is calmer and more matter-of-fact; 'glücklich' is more emotional and stronger.

Tom ist mit seiner Note zufrieden, obwohl er noch kleine Fehler gemacht hat.
Tom is satisfied with his grade, even though he still made small mistakes.
Sie ist glücklich, weil ihre Familie gesund ist.
She is happy because her family is healthy.