Article in English: Snapchat introduced updated video chat features in version 9.27.0.0, released March 2016. You'll need to be using this version or later of the Snapchat app in order to send and receive video calls. You can tap the button in the lower-left corner of the Snapchat Camera screen, or you can swipe from left to right. This will display all of your recent conversations. You can swipe any of your existing conversations from left to right to open them, or you can tap the New button at the top of screen and select the person you want to video chat with. This will begin calling the other person. Depending on their notification settings, they may need to be using the Snapchat app in order to see that they're receiving a video call. If the other person sees the notification that they're receiving a video call, they can choose to join your call or just watch. If they choose to just watch, you'll be notified that they've picked up but you won't be able to see them. If they select "Join," you'll see their video and they'll see yours. This will let you quickly switch between the front and rear-facing cameras. Both you and the recipient will be able to see emoji that you add. This won't end the call, but will stop you broadcasting video. To exit the call completely, close the conversation or switch to another app.

Summary in Vietnamese:
Đảm bảo rằng bạn đang dùng phiên bản mới nhất của Snapchat. Mở hộp thư đến Snapchat. Mở cuộc trò chuyện trong Snapchat với người bạn muốn gọi. Nhấn nút Video Camera ở dưới cùng màn hình tán gẫu. Đợi người kia nghe máy. Nhấn đúp vào màn hình để đổi máy ảnh trong khi gọi. Nhấn vào nút Stickers để thêm biểu tượng cảm xúc vào cuộc gọi. Nhấn nút Video Camera để dừng video.