Learn Dutch: Omdat de verlichting is geïnstalleerd, kan de catering beginnen. - Because the lighting is installed, the catering can begin.

This is the state passive. Using is plus the past participle shows that the action is completely finished and we are looking at the result: the lights are already up. If you used wordt geïnstalleerd, it would mean the installation is happening right at this moment.

Why are the verbs is geïnstalleerd pushed to the end of the first clause?

The conjunction omdat (because) always starts a subordinate clause. In a Dutch subordinate clause, the rule is that all verbs must go to the very end.

Why does the second half say kan de catering instead of de catering kan?

This happens because of inversion. The entire omdat clause counts as the first block of information in the sentence. The Dutch verb-second rule says the main verb (kan) must be in the second position, so it flips places with the subject (de catering).

Why is there a trema (two dots) on the 'i' in geïnstalleerd?

The trema tells you to pronounce the vowels in two separate syllables. Without it, the e and i would combine into the Dutch 'ei' sound (like in trein). The dots show it is pronounced 'ge-in-stal-leerd'.