Learn Dutch: Er is vaak ruzie in de groep. - There is often an argument in the group.

You could say Ze hebben vaak ruzie met elkaar (They often argue with each other). To say you are arguing with someone, Dutch uses ruzie hebben met. So you just add elkaar after met.

Why is it just ruzie and not een ruzie (an argument)?

In English, you have "an argument", which is a countable thing. In Dutch, ruzie is usually treated as an uncountable concept when talking about the general state of fighting or bickering. It is similar to saying "There is often conflict" in English.

Does er is work exactly the same as "there is" in English?

Yes! In this specific context, er is (there is) and er zijn (there are) are used to point out that something exists or is happening, just like in English.

Why does vaak (often) come after the verb here?

In a standard Dutch main clause, the verb must be in the second position. Since Er takes the first spot, the verb is must come next. Time adverbs like vaak typically follow right after the verb.