Learn German: Der Text wird verstanden, indem man ihn zusammenfasst. - The text is understood by summarizing it.

English often uses "by" plus an "-ing" verb to show how something is done. German doesn't have an exact equivalent to this "-ing" form. Instead, it uses the conjunction indem followed by a full subordinate clause with a subject (man) and a conjugated verb at the end (zusammenfasst). Literally, it reads like "by which one summarizes it".

Why does the first clause use wird verstanden rather than ist verstanden?

wird verstanden is the process passive. It emphasizes the action taking place: the text is actively being understood through the act of summarizing it. If you used ist verstanden (the state passive), it would describe the final state after the action is already fully complete, meaning the text is already understood.

What does the ihn refer to in the second half of the sentence?

ihn is the masculine accusative pronoun meaning "it" (or "him"). Here, it refers back to Der Text, which is a masculine noun. It is in the accusative case because it is the direct object of the verb zusammenfasst (the thing being summarized).

zusammenfassen is a separable verb. Why isn't it separated into fasst ... zusammen here?