開ける

In a sentence

• ドアを開ける。

  I open the door.

  Here, '開ける' is used in its basic sense, meaning 'to open,' and it refers to physically opening something tangible like a door.

• 窓を開けてください。

  Please open the window.

  In this sentence, '開ける' appears in the imperative form '開けて,' forming a polite request when combined with 'ください' to indicate opening a window.

• 箱を開けたら、中に手紙があった。

  When I opened the box, there was a letter inside.

  Here, '開けた' is the past tense of '開ける,' narrating an action in the past context where a box was opened.