Learn German: Wo ist der Junge? Wir treffen ihn jetzt. - Where is the boy? We are meeting him now.

In the first sentence, der Junge (the boy) is the subject. If we replaced it with a pronoun, it would be er (he). But in the second sentence, we (wir) are the ones doing the meeting, making the boy the direct object. Just like 'he' changes to 'him' in English, the German masculine pronoun er changes to the accusative form ihn when it is the direct object.

The English translation says 'are meeting', but the German just says treffen. Where is the 'are'?

German does not have a separate 'verb + -ing' form (the present continuous tense) like English does. Depending on the context, wir treffen translates to 'we meet', 'we do meet', or 'we are meeting'.

Does Junge end in an 'e' because it is a feminine word?

No, der Junge is masculine, which we can tell from the masculine word for 'the' (der). While many German words ending in 'e' are feminine, there are some common exceptions. Der Junge (the boy) and der Käse (the cheese) are masculine words you just have to memorize.

Could I change the word order and say Wir treffen jetzt ihn?