Mở Facebook. Đi đến ảnh mà bạn muốn tải xuống. Nhấp vào ảnh. Chọn ảnh. Nhấp vào Options (Tùy chọn). Nhấp vào Download (Tải xuống).

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?
Go to https://www.facebook.com/ in your browser. This will open the News Feed if you're logged into your Facebook account. If you aren't logged into your Facebook account, enter your email address (or phone number) and password in the upper-right side of the page to log in. Scroll through your News Feed until you find the photo that you want to download, or go to the profile of the person who posted the photo to find it.  You cannot save cover photos on Facebook. You can go to a person's profile