My scrollbars have disappeared or only show occasionally. How do I get them to display all the time?

Mac OS X (since 10.8) defaults to displaying scrollbars only when needed based on trackpad or mouse activity. If you prefer that scrollbars are always displayed, select System Preferences under the gray apple. 

Select the General Preference Pane. 

       

 

Click on the radio button next to Always in the Show Scroll Bars: section