I have a variable that holds a string of instuctions, for example:

str_instruct = "Add 6 cups of water in a pot : Bring water to boil "

now I display that string by doing:

arr_instruct = Split (str_instruct,":")
for i = 0 to UBound(arr_instruct)
    Response.Write (arr_instruct(i)&"<br>")
next

Now here is the quesiton. I have a textarea that allows me to add
further instructions.

How can I, after clicking a button "add", append to the end of the
string the content of the textarea with my test char ":" to the same var
(str_instruct), then have the page reload allowing me to see the new
string and have it displayed

Is this even possible?

The form action must point the page that is showing this output. Then you just concatenate the value from the textarea onto the string before you split it:

If Request.Form("myTextArea") <> "" Then
    str_instruct = str_instruct & ":" & Request.Form("myTextArea")
End If
arr_instruct = Split (str_instruct,":")
...

Peter
------------------------------------------------------
Work smarter, not harder.