"Our girls do not drink beer."
Translation:Fetele noastre nu beau bere.
I entered fetele noastre nu bea bere..that must be the masculine then with bea and beau feminine?
No, but "bea" is in third person, singular, and here you have to use the third person plural, which is "beau".
Fun (or sad) fact: Using the singular instead of the plural form is a common mistake among less educated, usually rural, native speakers. Fetele noastre nu bea bere sounds exactly like a very natural thing someone in that scenario would say.
Have a lingot for providing context that would be hard to find for non-natives! (But then again, have patience with your people! - If it was up to the educated people only, you would probably still speak Latin, along with the whole of the South of Europe, no need to learn Spanish. And we Germans would have probably adopted Latin, too. We all owe our culture to the unruly creativity of the "regular" folks! :)