It's a green app with a white phone icon on it. This tab is near the top of the screen. If WhatsApp opens to a conversation, first tap the "Back" button in the top-left corner of the screen. This will open the conversation in question. You can also tap the "New Message" button in the bottom-right corner of the screen and then select a contact to start a new conversation. It's the smiley-face icon on the left side of the chat bar that's at the bottom of the screen. You can tap a tab near the top of the emoji window to browse through emoji categories, or you can swipe left across the emojis to scroll through them. It's on the right side of the chat bar. This will send your emoji(s) to the conversation.

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Write a summary of the previous text in Vietnamese:
Mở WhatsApp. Nhấn CHATS (Trò chuyện). Nhấn vào một cuộc trò chuyện. Nhấn vào nút biểu tượng cảm xúc. Chọn một biểu tượng cảm xúc. Nhấn vào mũi tên "Send" (Gửi).