N3
次第
しだい
As soon as
用意が出来次第、僕に声をかけてください。
As soon as you get ready, please let me know.
Explanation
「次第」 has 2 uses
1As soon as
After the ます-stem: as soon as one thing is done, the next follows, common in business: 「準備ができ次第、出発します」.
準備が出来次第出発しますよ。
We will depart as soon as you are ready.
用意が出来次第、僕に声をかけてください。
As soon as you get ready, please let me know.
2Depends on
After a noun: 'it all depends on…': 「結果は努力次第だ」.
行くか行かないかは君次第だよ。
Whether you go or not will depend on you.
6人も乗れるかは車のサイズ次第だね。
Whether or not 6 people can fit will depend on the size of the car.
Mixed up with
The end of the sentence can never be past tense: you cannot say 「駅に着き次第、電話した」. Past events use 「〜たら」 or 「〜と」; for the future, 「駅に着き次第、電話します」 is correct.
Typical business mail: 「分かり次第お知らせします」 (I will let you know as soon as I find out).