"We teach boys and girls."
Translation:Pueros et puellas docemus.
The word -que (an "enclitic," like the -ne used to ask a yes/no question, it's not a word by itself, but must be attached at the end of a word) is another way to say "and."
We use "et" (like Engl. "and") by inserting it 'between' the two connected items: boys and girls: pueri et puellae (in any case: pueros et puellas, etc.) he talks and shouts: loquitur et clamat
-que will come at the end of the 2nd item: pueri puellaeque / pueros puellasque; loquitur clamatque.
(I think of it as: A et B , but A Bque
There isn't just one "plural" form of a noun in Latin; there are 5, for the different "cases" (or functions).
Pueri is THEY the boys, as a plural subject. Pueros is THEM the boys, as a plural object (here, object of the verb, or 'direct' object: we teach THEM).
There are also: puerorum, OF the boys, when they possess something; and two different uses of pueris, one (dative), TO/FOR the boys (as indirect object), and ablative pueris as object of certain prepositions (a pueris, by the boys, cum pueris, with the boys, etc.).
The noun "girls" belongs to a different declension (or group of nouns with a specific pattern of endings): puellae, puellarum, puellis, puellas, puellis.