what is the difference between scheduled start and start columns? (and for sheduled finish and finish)

See the field reference:

https://support.office.com/en-gb/art...6-92d475803d39

The fields were added in Project 2010 because of manually scheduled tasks.

By the way, you have posted a great many questions to this forum. A "thank you" now and again would be appreciated.

thank you so much !
i thought i did that sometimes... thanks again for the help....

You're welcome.