诉 is a bound form (b.f.) that never appears alone in modern Chinese — it always combines with another character to form a compound. It has two main sense clusters: 'tell, relate, inform' (as in 告诉 'tell', 诉说 'relate, recount') and 'accuse, sue, appeal' (as in 诉讼 'lawsuit', 控诉 'accuse', 上诉 'appeal', 起诉 'sue'). When learning vocabulary containing 诉, focus on the full compound rather than the individual character.