"match" function: what to do with the ( ) result?

The "match" function returns a result in ( ).

I would have liked to use the value returned by "match" as an index, but if I try to assign the "match" result to a variable, the variable is flagged as "undifined" when called further down the road.

"Help" is not much help on that.

Is there a way to make usage of the (value) returned by "match", or can this function be used for informational purpose only?

Thank you.