I have this column that behaves strangely. I try to put a value into it and instead comes this same date value every time.
18/3/20 that I was using when I was trying to get the date thing to work.
I have tried deleting many cells in the column but it still does it. Just that column. No other.
Why is that?practiceassessment.ods
Please provide a sample file, since nobody can analyze your settings from the details given - and please see my answer to your question How To Enter Dates & How to Know What's in a Cell? (-> Clear all formatting using CTRL+M).
okay. I edited the question and attached the sheet. It is column C that it happens in.
Thanks for your date entry answer. Great stuff. 
The file you have provided is just an empty spreadsheet. This doesn’t demonstrate anything. Did you CTRL+M before your uploaded? If yes - my comment wasn’t meant that you need to do that, but a potential solution and if you did that before you have uploaded and I now notice that it is an empty spreadsheet, than this is the solution.
File provided has Total editing time of 00:00:00.