Linux – What language does the Konsole window run and what does it do?

1. How do I store the result of an expression in a variable?

   echo "hello" > var1
   

2. Can I do something like this too?

   var1.substring(10,15);
   var1.replace('hello', '2');
   var1.indexof('hello')
   

Postscript. I have tried to google search but without success.

As @larsmans commented, Konsole is a terminal emulator that in turn runs a shell.
On Linux, this is usually bash, but it can also be something else.

Find out which shell you are using and print the man page.

echo $SHELL         # shows the full path to the shell
man ${SHELL##*/}    # use the rightmost part (typically bash, in linux)

For a general introduction, use wikipedia entry on the Unix shell or GNU Bash refererence

Some specific answers:

var1="hello"
echo ${var1:0:4}         # prints "hell"
echo ${var1/hello/2}     # prints "2" -- replace "hello" with "2"

At the risk of showing off:

index_of() { (t=${1%%$2*} && echo ${#t}); }  # define function index_of
index_of "I say hello" hello
6

But this goes beyond simple shell programming.