Guide

1. Inside your Microsoft Excel worksheet, find and select the cells that go along the lines you wish to bold.

2. After that, head over to the top menu bar and then click the 'Borders' option under the Home tab.

3. Choose 'More Border Styles' from the list of options.

4. Under the Border Style section, find and click the 'Thick Line' option.

5. Subsequently, choose the specific border you prefer to use.

6. After completing these steps, the lines of the selected cells will appear in bold.