say you have a string like this:
var s="our string"
and you want to capitalise the s in string.
you can change with this:
s = "S"
you can treat a string like an array, and alter it's values by the index of the characters.
so with "our string"
o == index 0
u == index 1
r == index 2
== index 3
s == index 4
there are also a bunch of helper functions in the String class:
so the find the first instance of "s" within the string you could call:
var s_index = find ("s", from=0)
so you could also call
s = s.replace("s", "S")
which would replace all instances of s with S