Self Doubt

Question

We know that Relational Algebra is $Procedural$ whereas TRC and DRC are $Non-Procedural$ querry languages. But what exactly differentiates them? Please explain using some example.

In Relational Algebra we give what to retrieve and how to retrieve but in TRC or DRC we just specify what to retrieve. I am unable to find any convincing example for it.

I have also referred below links but i doubt as it is not given in any standard book or authentic source

1. https://stackoverflow.com/questions/47434409/procedural-and-non-procedural-query-language-difference
2. https://stackoverflow.com/questions/32837278/difference-between-relational-algebra-and-relational-calculus/32841232#32841232

Please explain using some example