current cells in use on spreadsheet are outlined in red w/small red box in cell upper left corner. How to make red outline go away & how to prevent it from happening again? 2nd time happened, appears when spreadsheet is opened.

Spreadsheet contains both text and numbers and formulas. Red outline only appears on those cells recently in use or just used.

Btw please formulate shorter question summaries.

You seem to have switched on Change Tracking, switch off with menu Edit → Track Changes → Record.

I did send a Thank You note the day I received your answer, I hope you got it. I took your advice and fixed the problem - so again, Thank You.