>I was a bit confused about string and String. I see now that "string" is used to declare a string variable, whereas "String" originates from a class, and is used to do formatting, but from which class? as in String.Format().

BTW - they're the same class (so it doesn't matter). You can write code like this and it's all equivalent:

string myString = "Hello";
System.String myString = "Hello";

string format = string.Format("{0} there.", myString);
string format = String.Format("{0" there.", myString);
System.String format = string.Format("{0} there.", myString);