This is the yellow icon with a white ghost in it. Tapping on it will open Snapchat’s camera interface. This will bring up the Chat menu, from which you can open individual chats. You won't be able to save a chat that you've already opened and closed before. This will open the chat conversation. The background will turn gray, and the phrase "Saved" should pop up on the left side of the chat.  You can save both your recipient's chats and your own chats. You can tap and hold again on the same chat to unsave it. When you leave the conversation, the unsaved chat will disappear. Your saved chat will appear at the top of the chat window, and will stay there unless you unsave it.

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Write a summary of the previous text in Vietnamese:
Mở Snapchat. Vuốt sang phải. Vuốt mục trò chuyện mà bạn muốn lưu sang bên phải. Chạm và giữ tin nhắn bạn muốn lưu. Xem tin nhắn đã lưu bằng cách mở lại cuộc trò chuyện bất cứ lúc nào.