Use of FFT function in Matlab 2013 b

Hello, I am trying to convert time domain data of pressure signal to frequency domain. I have data in excel file with each variable in separate columns. Both variable (time and pressure) were imported to Matlab as column vectors using import tool. But while using fft function (fft(pressure)) to generate frequency domain data, I get some random values. I've attached both mat file and excel output.

Am I doing this correctly ? If yes, how to interpret the fft data ?

If I want to get fft withing a specific frequency range and resolution, how to do ?

Best Regards Saumya

[Saumya]

I tried to generate FFT for the data. but in the result I am getting two complex values. Attached are input time data and output fft data. Please help to interpret the same.