When 次第 follows a ます-stem (the form before ます), it means 'as soon as' or 'right after' something happens. It emphasizes that the second action occurs immediately after the first event is completed. This is common in formal or business contexts, such as reporting progress or giving instructions. For example, 資料ができ次第、送ります means 'I will send it as soon as the materials are ready.' It sounds more polite and formal than using たら or とすぐに.

When 次第 follows a noun, it means 'depends on' or 'is up to'. For example, 成功するかどうかは努力次第だ means 'Whether we succeed depends on our effort.' This usage is also somewhat formal but common in both speaking and writing. The noun can be a person (like あなた) or a thing (like 天気).

Note that 次第 is not used in casual conversation as often as in formal speech. In casual settings, you would use すぐに or によって決まる instead.