Some of your question is a little hard to understand, but in the examples you've given, there is no difference between "on" and "about." Examples: 1) We went to the meeting about the environment. 2) We went to the meeting on the environment. Those sentences both mean the same thing. However, "on" and "about" don't always mean the same thing. "On" usually points to something specific, like a location. "About" usually means the subject of something, or something less specific. Here are two more examples that show the difference: 1) We had a party on New Year's Eve.-- This party was held at a specific time: New Year's Eve. 2) We arranged to meet at about 2:00PM. -- This meeting is supposed start sometime around 2PM, rather than exactly at 2PM.