What uses curly braces containing a number that indicates the desired position for a variable in a list that follows a string used for formatting purposes?

In programming technology it used as common and some place it is varies.

If variable declared as string data type position represents the character of the string. If variable declare as integer data type position represent as cell reference.

Curly braces containing a number indicates the position of character in it data type is string

At the same it also indicates the position of a array.

Dim a as string = "HELLO"

A (2) - it is represents "L" where it started 0 optional bas

Dim a (10) as integer = (1,2,3,4,5,6,7,8,9,10)

A (2) - it represented array cell position answer is "3".