Try posting an example piece of code to make your problem a little clearer,
Normally though you use the error connections (the pink wires) on the VI's to control the flow of data, you then place the voltage read operation after you have 'set' your frequency.
You could think of the error connection a bit like a rail track, where the train has to visit each station (VI) in turn.
You could also use a sequence as well, although it's probably a bit unecessary if you use the error connections to control the order in which VI's are executed.
