Hello & welcome to the forum!
Live rock is used for refugiums , food source, tank establishment and other matters in saltwater tanks. That said, Its not advisable to add salty live rocks to a freshwater tank. Most freshwater fish do not tolerate saltwater set ups.
If you wan the rocky look like that in your freshwater tank, I"d advise a trip to any given pet store around you either get normal, non calcareous rocks or plastic versions to decorate your tank with (these are also cheaper for you then purchasing live rock).