glücklich
happy
Feeling a state of joy, satisfaction, and emotional well-being.
Sie war sehr glücklich, als sie die gute Nachricht hörte.
She was very happy when she heard the good news.

happy / lucky
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happy
Feeling a state of joy, satisfaction, and emotional well-being.
Sie war sehr glücklich, als sie die gute Nachricht hörte.
She was very happy when she heard the good news.

'Glücklich' is the adjective formed from the noun 'das Glück'. Since 'das Glück' can mean both 'happiness' and 'luck', 'glücklich' also has these two main meanings: 'happy' and 'lucky/fortunate'.
Ich hatte Glück und habe gewonnen, jetzt bin ich glücklich.
I was lucky and won; now I'm happy.
When you want to state the reason for the joy, you often use the preposition 'über' with the accusative. To express satisfaction with something, use 'mit' and the dative.
Er ist glücklich über das gute Ergebnis.
He is happy about the good result.
When 'glücklich' describes a person's feeling, it means 'happy'. When it describes a situation, event, or coincidence, it means 'lucky' or 'fortunate'.
Der glückliche Gewinner konnte sein Glück kaum fassen.
The lucky winner could hardly believe his luck.
successful
'glücklich' and 'erfolgreich' can both describe that something turned out well. 'erfolgreich' clearly says that a goal was achieved. It fits well with exams, projects, conversations, or plans. In this context, 'glücklich' can mean that something ultimately went well or favorably, often with some luck. Learners confuse the words because success can make people happy. But 'erfolgreich' describes the result; 'glücklich' describes either a feeling or a particularly good outcome.

Nach einem schwierigen Start nahm die Reise doch noch ein glückliches Ende.
After a difficult start, the trip did have a happy ending after all.
Die Klasse bereitet sich gut vor und besteht die Prüfung erfolgreich.
The class prepares well and successfully passes the exam.