You can only do this within your own custom tool objects.
(You cannot cause the display the coordinates during native tool operations. Some native however will display the coordinates in the VCB aka Measurements box. Some are absolute and some are relative. It just depends upon the tool.)
See this example extension from the SketchUp Development Team:
- Utilities Tools extension
In the "utilitiestools.rb" file, look at the TrackMouseTool class.
To code for SketchUp, … you need to understand how SketchUp works, then you need to learn core Ruby, and then how the SketchUp Ruby API extends Ruby.
To create webdialogs, you also need to know HTML, CSS and Javascript.
So your question is vague. We do not know what kind of programming experience you have, and the forum is not a good place to post a major tutorial on programming.