The Insert method is able to add one string into another. This method expects an index from the beginning of the string, counting from 0, and a string to insert:

$string = 'The letter of the alphabet is a' 
$string.Insert(4, 'first ')  # Insert this before "letter", include a trailing space 

The Remove method removes characters from a string based on a start position and the length of the string to remove:

$string = 'This is is an example' 
$string.Remove(4, 3) 

The previous statement removes the first instance of is, including the trailing space.