Usually line feed can be input by pressing [Enter] key. However, when you end the wraparound of the text, you need to input a special line feed. For that case, the type of line feed can be selected in this dialog.
[Normal Line Break] radio button
This is a normal line feed input by pressing [Enter] key.
[Move Vertically Down to a Clear Left Margin] radio button
This button will end the wraparound of the text to an image or a table that is left justified.
[Move Vertically Down to a Clear Right Margin] radio button
This button will end the wraparound of the text to an image or a table that is right justified.
[Move Vertically Down Until Both Margins Are Clear] radio button
When both left and right justify exist at the same time, the wraparound to these both will be ended.