As shown in the picture beside, there are paragraph that are not with red striped and another paragraph show different things. It is caused by the language setting that do not conform with the typed text. So the program shows an error correction which is marked with a red line.
Almost every word processing software has this feature and the free Open Office Writer too. So, to eliminate the red line, match the typed sentences with the language used in software. Follow the following interactive tutorials to make it more clear.
Related Open Office Tutorial