Learn Dutch: Het hangt ervan af of iedereen meegaat. - It depends on whether everyone comes along.

The phrase for "to depend on" is afhangen van. Because the thing it depends on is an entire clause starting with of, Dutch uses a placeholder. Instead of saying "van of", you use ervan (meaning "of it") to bridge the main sentence and the subclause.

Why are hangt and af separated in the first part of the sentence?

Afhangen is a separable verb. In a main clause, the core verb (hangt) takes the second position, and the prefix (af) goes to the end of that clause. That is why "it depends on it" translates to het hangt ervan af.

Doesn't the word of usually mean "or"?

It does! However, of is also the Dutch word for "whether" or "if" when you are introducing an indirect question or a condition. That is exactly how it is used in this sentence.

Why is meegaat placed at the very end as a single word?

Meegaan (to come along) is a separable verb. Because the word of introduces a subordinate clause, all verbs are pushed to the end. When a separable verb is pushed to the end of a subordinate clause, its prefix (mee) and the verb (gaat) recombine into one single word.