Learn Italian: Se si sbaglia, ci si scusa sempre. - If one makes a mistake, one always apologizes.

The verb for to apologize is the reflexive scusarsi. To make a reflexive verb impersonal (meaning 'one apologizes'), you need both the reflexive pronoun (si) and the impersonal pronoun (si). Since Italian avoids the awkward sound of si si, the first one changes to ci, giving us ci si scusa.

Why does the first half of the sentence just use si (si sbaglia) instead of ci si?

Sbagliare (to make a mistake) is a standard, non-reflexive verb here. Because it doesn't already have its own reflexive pronoun, it only needs the single impersonal si in front of it to mean 'one makes a mistake'.

Could I translate this as 'If you make a mistake, you always apologize' instead of using 'one'?

Yes, absolutely! In spoken English, we rarely use 'one' and instead use the generic 'you' (or sometimes 'people' or 'we'). In Italian, the impersonal si and ci si structures are the most natural way to express this general 'you'.

Why is sempre placed at the very end of the sentence?

In Italian, adverbs of frequency like sempre (always) generally go immediately after the conjugated verb. Here, it naturally follows the verb scusa.