Click in a section or select multiple sections. On the Layout tab, in the Page Setup group, click Line Numbers. Click Line Numbering Options, and then click the Layout tab. In the Apply to list, click Selected sections. Click Line Numbers. Select the Add line numbering check box, and then select the options that you want. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.