chr$() -- accepts a number and returns the character at this position within the ascii charset
The chr$-function is the opposite of the asc-function. It looks up and returns the character at the given position within the ascii-charset. It's typical use is to construct nonprintable characters which do not occur on your keyboard.
Nevertheless you won't use chr$ as often as you might think, because the most important nonprintable characters can be constructed using escape-sequences using the \-character (e.g. you might use \n instead of chr$(10) wherever you want to use the newline-character).
This will print the letters 'a' and 'b' in different lines because of the intervening newline-character, which is returned by chr$(10).