Mở Gmail. Nhấn vào nút hình ☰ ở góc trên bên trái màn hình. Cuộn xuống và nhấn vào Settings. Nhấn vào General settings (Cài đặt chung) trên trang Settings. Cuộn xuống và nhấn vào Confirm before sending (Xác nhận trước khi gửi).

I'm interested in that, but I only have a few mins. Can you give me at most the first 500 characters of a detailed explanation in English about that?
Tap the Gmail app, which resembles a red "M" on a white background. This will open your Gmail inbox if you're logged in. If you aren't logged in, you'll need to enter your email address and password when prompted. It's in the top-left corner of the screen. Doing so prompts a pop-out menu. This option is at the bottom of the pop-out menu. The Settings menu will open. You'll find this on the Settings page. It's at the bottom of the page. This will ensure that any email you send will have to be con