When you're sending a quick Facebook comment, it is generally acceptable to write your message in one unformatted paragraph. If you want to create more structure in your post or comment, indicate a new paragraph by putting a space between two lines of text. Depending on which field you are in, the process of inserting a new line is slightly different. If you mess up, comments and posts can always be deleted and redone.
Click inside of the "What's on your mind?" field at the top of your Facebook homepage. Type your first line and hit the "Enter" key to move down to the next line. Hit the "Enter" key a second time to move down again and type new text – an empty line will appear between the two lines of text.
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Click inside the "Write a comment" field beneath any post or link on your Facebook wall, or the wall of a friend.
Hit the "Shift" key and then "Enter" to move down to the next line. Repeat the process to move down again and begin to type new text. Moving down to a new line twice creates a blank line between your text.