In HTML form by setting Absolute file path setting means full URL of a file to be given on the src attribute i.e full internet file path.
In HTML form by setting Relative file path setting means relative to the current page to be given on the src attribute i.e relative file path. The following example will observe that the root folder of the .png file path setting.
In the following example will observe that the current folder of the .png file path setting.
In the following example will observe that the path pointing one level above to the current folder of the .png file path setting.
In the following example will observe that the path pointing two level above to the current folder of the .png file path setting.
With all these examples are very important to identify the path settings. All you will learn these by practice very well manner to understand. In suggestion in real time scenarios you need to understand and best usage relative paths of file path addressing. In this situation if you given as absolute path of your local drive and folder paths it may different on server folder drive structures where your application hosting that web site.