New to AutoIt, not understanding ConsoleRead/Write function

Hi!
 
"Console Read: Read from the STDIN stream of the AutoIt script process"
I'm not sure what the STDIN stream is but my guess is it's a stream which tracks what happens when I run a script. Like a log file.
 
However, I can not wrap my mind around how these two functions work: ConsoleRead, ConsoleWrite
 
Let me illustrate with an example:

Local $var=consolewrite("hi")
MsgBox(1, "", $var)

This is working perfectly fine.
 

Local $var2=consoleread()
consolewrite("hi") ;with this I thought I wrote "hi" to the console, which I will then be available to read with consoleread.
MsgBox(1, "", $var2)

This just returns a blank msgbox.

Did I not write "hi" to the console or does consoleread not read what's in the console?

Sidequestion: How do you all find out what's going wrong with your scripts? Read the console at bottom of autoit? All I see there is "Exit code: 0" which doesn't help me much. Anywhere I can find a list of exitcodes and their meaning?

Slightlyrelated to first sidequestion: is the value of  the @error macro same as the consoles exitcode? If not, do you ppl. always send @error in a msgbox to see what went wrong, or is there another way of doing this?

Thanks on beforehand