* Noun: This is the most common usage. It refers to a group of people assembled for religious worship.
* Verb: It can also be used as a verb, meaning "to gather in a crowd or assembly." For example, "The protesters congregated outside the government building."
To determine the correct part of speech, look at the context of the sentence.
Let me know if you have an example sentence, and I can tell you the part of speech for "congregation" in that specific case!