There are two ways to add help text in a lightning component. First, you can use the standard lightning.helptext base component or you can create a custom CSS file to add the help text to the component. When a user hovers over an input box, help text displays. It can display information about the field and it’s the exact same for all records. If you have a radio button that allows users change their settings, the help text will be displayed as a popover whenever they click it.
How to Add Help Text in a Lightning Component