If something is immediately obvious, it can be seen or understood without any delay. The cause of the accident was not immediately apparent. = instantly
If something happens immediately, it happens without any delay. He immediately flung himself to the floor Ingrid answered Peter's letter immediately
Immediately is used to indicate that someone or something is closely and directly involved in a situation. The man immediately responsible for this misery is the province's governor
If one thing happens immediately something else happens, it happens after that event, without any delay. Immediately I've done it I feel completely disgusted with myself
without delay or hesitation; with no time intervening; "he answered immediately"; "found an answer straightaway"; "an official accused of dishonesty should be suspended forthwith"; "Come here now!"