直ちに is an adverb that means 'immediately' or 'without delay'. It is more formal than すぐに, so you will often hear it in public announcements (for example, on a train: '直ちにご連絡ください') or read it in official documents and news. It carries a sense of urgency and responsibility, so it is commonly used with verbs like 連絡する, 中止する, 避難する, and 報告する.

You can think of it as the word a company president or a train station officer would use, not something you'd say to a friend. For everyday 'right now', use すぐに or いますぐ. 直ちに can also mean 'directly' in a logical connection (e.g., 結果に直ちに影響する), but that is a secondary use.

In a sentence, put 直ちに right before the verb or verb phrase, and keep the ending formal (ます form or plain written form). It is not used in casual speech.