zusammenfassen
to summarize
To present the most important information from a text, speech, or event in brief form.
Können Sie die Ergebnisse der Studie bitte kurz zusammenfassen?
Could you please briefly summarize the results of the study?

to summarize / group
Loading your saved state.
to summarize
To present the most important information from a text, speech, or event in brief form.
Können Sie die Ergebnisse der Studie bitte kurz zusammenfassen?
Could you please briefly summarize the results of the study?

This verb is made up of 'zusammen' (together) and 'fassen' (to grasp). 'Fassen' can mean 'greifen' (to grasp). So 'zusammenfassen' literally means 'to grasp together'—either you gather the most important ideas together (summarize), or you combine people into a group (group).
Er fasste die Kernaussagen des Artikels in drei Sätzen zusammen.
He summarized the key statements of the article in three sentences.
'Zusammenfassen' (to summarize / group) is a separable verb. In a main clause, the prefix 'zusammen' (together) goes at the end. In a subordinate clause and in the infinitive with 'zu', the parts stay together.
Der Sprecher fasst die Diskussion am Ende zusammen.
The speaker summarizes the discussion at the end.
In the meaning 'summarize', the verb is often combined with words like 'Ergebnisse' (results), 'Punkte' (points), 'Inhalt' (content), or 'Text' (text). A very common fixed phrase is 'Zusammenfassend lässt sich sagen, dass ...' (In summary, it can be said that ...).
Fassen Sie bitte die wichtigsten Punkte der Besprechung zusammen.
Please summarize the most important points of the meeting.
You can recognize the meaning from the object of the sentence. If it is about information, ideas, or texts, 'zusammenfassen' (to summarize / group) is meant in the sense of 'summarize'. If it is about people or concrete objects, it means 'to combine into a group'.
Ich fasse die Argumente für dich zusammen.
I'll summarize the arguments for you.
to separate
'trennen' and 'zusammenfassen' are clear opposites when it comes to groups, parts, or areas. 'trennen' means separating or distinguishing things from one another. Here, 'zusammenfassen' means combining several individual things into a group or unit. For example, you can separate tasks by topic or group several small tasks into one package. Important: 'zusammenfassen' can also mean briefly restating the content of a text; that meaning is not the opposite of 'trennen'.

Im Büro fassen wir die kleinen Termine zu einem gemeinsamen Termin zusammen.
At the office, we group the short appointments into one shared appointment.
Bitte trenne Papier und Plastik, bevor du den Müll rausbringst.
Please separate paper and plastic before you take out the trash.