>>2935694
>need help

you sure do
a scope is a super duper tool to measure voltage, frequency, shape of waveform, distortion, duty cycle etc etc etc
FFT is a special feature to show off the spectrum of frequencies found in the signal
it makes no sense to use the FFT function for anything other than that
what you need are video tutorials to show you how to do what you want
luckily youtube has over 9000 such videos
as