Learn Dutch: De foyer is versierd, dus zijn we klaar. - The lobby is decorated, so we are ready.

This sentence uses the "state passive" (toestandspassief). If you used wordt versierd (is being decorated), it would mean the action is happening right now—someone is actively putting up balloons or banners. By using a form of zijn (is) plus the past participle (versierd), you are describing the resulting state: the action of decorating is already finished, and the lobby currently sits in a decorated state.

Why doesn't the past participle versierd have a ge- at the beginning?

The infinitive verb is versieren (to decorate). Because it starts with the inseparable prefix ver-, it does not get an extra ge- in its past participle form. This rule applies to all verbs starting with inseparable prefixes like be-, ge-, her-, ont-, and ver-.

Why is the word order zijn we klaar instead of we zijn klaar?

The word dus (so/therefore) is acting as an adverb that takes up the very first position in the second clause. In Dutch main clauses, the verb must always come second. So, zijn takes the second position, which pushes the subject (we) to the third position. Note: In casual speech, you might sometimes hear people use *dus without changing the word order, but this inversion is the standard rule.*