You did not provide very much information so any response will involve some guesses.
Graphs have a histogram plot which can be selected by clicking on the little plot window of the Plot Legend. On the Mathematics >> Probability and Statistics palette are several VIs for generating histograms.
Are your measurements in frequency units or do you need to process some other kind of data to get frequency? Many Fourier Transform and statistics VIs are available. Choose the one which does the type of calculations you need.
The Mathematics palette has an entire sub-palette devoted to curve fitting.
Lynn
