Learn German: Wir feiern Ostern zusammen. - We celebrate Easter together.

Just like in English, most holidays in German are used without an article. You simply say Ostern (Easter), Weihnachten (Christmas), or Neujahr (New Year).

How do I say 'Easter is in April' to practice this lesson's month vocabulary?

To say that something happens in a specific month, you use the word im (a contraction of in dem). So, you would say: Ostern ist im April.

If I want to say we do something 'at Easter', what preposition do I use?

To say 'at Easter' or 'for Easter', you can use either zu Ostern or an Ostern. Both are correct and very common in everyday German.

Why does zusammen go at the very end of the sentence?

In standard German word order, the direct object (Ostern) usually comes before adverbs that describe how something is done, like zusammen (together).