I'm trying to say: at the party, Anna and her father argued about Annas behavior.. so far I have:

A la fiesta, Anna y su padre rineron acerca de la conducta de Anna.
but A, the first word, is wrong and so is the verb ending..? What is wrong with it?

Rather than "at" the party, perhaps, "during?"

Durante (En) la fiesta, Ana y su padre arguyeron de (OR acerca de OR sobre) la conducta de Ana.

Only use "a" when there is a verb of motion "toward" such as ir, venir, etc.

reñir is more "to fight"

Sra

The mistake in your sentence is that you have used the wrong form of the preposition "a" at the beginning. In Spanish, when indicating the location or time of an action, you should use the preposition "en" instead of "a." So the correct form would be "En la fiesta."

As for the verb "rineron," the correct verb to use in this context would be "discutir" which means "to argue." Therefore, the correct sentence would be:

"En la fiesta, Anna y su padre discutieron acerca de la conducta de Anna."

To construct this sentence, you can follow these steps:
1. Start with the location of the action, in this case, "En la fiesta" meaning "At the party."
2. Include the subject of the sentence, which is "Anna y su padre" meaning "Anna and her father."
3. Choose the appropriate verb for the action, which in this case is "discutieron" meaning "argued" in the past tense.
4. Finally, add the preposition "acerca de" to convey the meaning of "about" or "regarding" in relation to Anna's behavior, and then include the noun "la conducta de Anna" which means "Anna's behavior."

Putting it all together, the correct translation is: "En la fiesta, Anna y su padre discutieron acerca de la conducta de Anna."