Learn German: Er zündet eine Kerze an, um etwas zu sehen. - He lights a candle to see something.

It belongs to the separable verb anzünden (to light or ignite). In a regular main clause, the prefix (an) splits off from the verb stem (zündet) and moves to the very end of that clause.

How does the um ... zu structure work here?

The phrase um ... zu translates to "in order to". It expresses a goal or purpose. The word um starts the clause, and zu comes directly before the infinitive verb (sehen) at the very end.

Could we use damit (so that) instead of um ... zu in this sentence?

Yes, you could say ..., damit er etwas sieht. However, when the subject is the same in both halves of the sentence (here, er), it is much more common and elegant to use um ... zu because you don't have to repeat the subject.

Can I use was instead of etwas here?

Yes! In casual, spoken German, was is frequently used as a short version of etwas. Saying ..., um was zu sehen sounds very natural in everyday conversation, though etwas is preferred in formal writing.