for the 737 FMC in the perf init page under key5R it shows Datalink then NO COMMwhat is this please, i've read the manual and can see nothing on it

Datalink is for route request, ACARS, wind request, things like that.In the real world you'd enter your flight number eg UAL1234 into the FLIGHT NO line and press RTE REQUEST if avaliable; this would upload your route simmilar to what COROUTE doesFlight Sim has no way of request a route or wind data that can be loaded into the CDU. Same for real world style ACARS