MSPTrainer answered very well. I only add that when you give an activity some progress of percent complete greater than zero...the planned date at the time of the progress entry becomes the "Actual" start date. Also when you give an activity 100% complete the Finish date at that time of entry...
When I enter specific To: and From: dates in the "Timescale" section of the Print dialog box, these specified dates do not stay....projects does not retain them..they revert back to a previous setting. I am trying to start a new project starting January 1, 2010 and completing January 1, 2011...