How to update am Item of DateTime type?

Setup, Configuration and Use Scripts & Rules
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In addition to also tried ECMAScript and Blocky script. Not clear how to get the current date time into a DateTime Item.

I looked at this page: DateTime Conversion (openHAB 3.x)
But I am not clear how this helps me.

I also looked at this, but it is not clear how this could help me: OH3 Setting current DateTime to a custom item in a rule - #2 by muelli1967

I would have thought it would be simple to record when something happened and display it. Am I missing something really obvious?