
zocken
to game
Colloquial for playing video games or computer games intensively, often over a longer period of time.
Am Wochenende habe ich mit meinen Freunden die ganze Nacht gezockt.
At the weekend, I gamed with my friends all night.
to game / gamble
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to game
Colloquial for playing video games or computer games intensively, often over a longer period of time.
Am Wochenende habe ich mit meinen Freunden die ganze Nacht gezockt.
At the weekend, I gamed with my friends all night.

to gamble
Colloquial for gambling, often with high risk and in the hope of making a quick profit.
Er geht jeden Freitag ins Casino, um beim Poker zu zocken.
He goes to the casino every Friday to gamble at poker.
'Zocken' is a colloquial word in both meanings. In formal contexts, you would instead use, for example, 'Computerspiele spielen' (to play computer games) or 'Glücksspiel betreiben' (to gamble).
Er zockt am liebsten Strategiespiele am PC.
He likes gaming strategy games on the PC best.
The context reveals whether video games or gambling is meant. Words like 'Konsole' (console), 'online', or 'Computer' point to video games. Words like 'Casino', 'Geld' (money), or 'Poker' point to gambling.
Wir haben online bis tief in die Nacht gezockt.
We gamed online until late into the night.
In the context of video games, 'zocken' is often used without a direct object. Typical phrases are 'eine Runde zocken' (to play a round), 'mit Freunden zocken' (to game with friends), or 'die ganze Nacht durchzocken' (to game all night long).
Lass uns am Wochenende eine Runde zusammen zocken!
Let's game together for a bit at the weekend!
When it is about gambling, the stake is often expressed with the preposition 'um' plus the accusative. The activity itself is often described with 'beim' + dative.
Sie zocken jeden Samstag um kleine Geldbeträge.
They gamble for small amounts of money every Saturday.
to play
Both words can refer to video games or gambling. „Spielen“ is the neutral general term and also fits in factual statements. „Zocken“ is much more colloquial and often emphasizes prolonged, intense gaming when referring to video games; in gambling, it often suggests greater risk, although that is not always intended.

Die Jugendlichen zocken nach dem Essen noch stundenlang Videospiele.
The teenagers keep gaming for hours after dinner.
Die Kinder spielen nach dem Essen noch eine Runde Videospiele.
The children play another round of video games after dinner.