You can place a comment in a .cnc file in two ways.
You can insert // at the start of your comment and all text from the first / to the end of the line is ignored by the post. The // may be anywhere on the line, including on a line by itself. For example:
// This is a comment. No calculation is done.
You can also insert a # as the first character in an expression. For example:
[# This is a comment. No calculation is done.]