rocken
to rock
To play or perform rock music.
Die Band rockte auf der Bühne und begeisterte das Publikum.
The band rocked on stage and thrilled the audience.

to rock
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to rock
To play or perform rock music.
Die Band rockte auf der Bühne und begeisterte das Publikum.
The band rocked on stage and thrilled the audience.

You can recognize the meaning of 'rocken' (to rock) from the object. If it refers to a stage, a concert, or a band, it is about music. If it refers to a task or challenge, the colloquial meaning 'to do something really well' is meant.
Die Band hat gestern Abend die ganze Stadt gerockt.
The band rocked the whole city last night.
The meaning 'to master something' or 'to be great' is colloquial. Use it in informal situations with friends, but avoid it in formal emails or official conversations.
Macht euch keine Sorgen, das Spiel rocken wir!
Don't worry, we'll rock this game!
In the colloquial meaning, 'rocken' (to rock) is often combined with challenges. Typical expressions are 'die Prüfung rocken' (to rock the exam), 'das Projekt rocken' (to rock the project), or simply 'das Ding rocken' (to rock this thing).
Ich bin gut vorbereitet und werde das Vorstellungsgespräch morgen rocken.
I'm well prepared and I'm going to rock the job interview tomorrow.
When it is about music, the object of 'rocken' (to rock) is often the place where the performance happens. Typical phrases are 'die Bühne rocken' (to rock the stage) or 'das Festival rocken' (to rock the festival).
Am Wochenende hat eine lokale Band auf dem Stadtfest die Bühne gerockt.
At the weekend, a local band rocked the stage at the town festival.
to play
'spielen' and 'rocken' can both refer to music. 'spielen' is the normal word when someone uses an instrument or makes music. 'rocken' only fits when it is about rock music or when a band performs with a lot of energy. Learners may confuse the words because you can say: a band 'spielt' (plays), and a rock band 'rockt' (rocks). But 'spielen' is neutral and much broader. 'rocken' sounds more casual and more intense.

Die Band rockt am Samstag auf dem Stadtfest.
The band is rocking at the town festival on Saturday.
Lena spielt seit drei Jahren Gitarre.
Lena has been playing guitar for three years.