You need to think about the steps necessary to achieve what the code does!

var 
str:string[10]; 
 

Think about what that actually does - in terms of code and/or data - on the microcontroller.

IF you want to duplicate the implementation precisely, you will need to consult your (Pascal?) Compiler Manual to determine how it represents strings;
IF you just want to get similar behaviour, you can choose your own string representation...

Note that (I think) 'C' uses a different string representation from Pascal...

str:='Hello'; 
 

Again, what does that actually do - in terms of code and/or data - on the microcontroller?

It's going to have to handle each character in the string in turn, and needs some way to determine the end (or length) of the string - doesn't it...?