By default, when you hit the Enter key in a web editing program, the system thinks you want to start a new paragraph, so it drops you down two lines. But if you try to backspace or delete one of them, you can't. It takes you back to the end of the previous line.
If you want to drop to the next line without starting a new paragraph, you can hold down the SHIFT key while pressing Enter. This inserts a line break in the HTML, starting a new line within the same logical paragraph.