Watch out for those online sources (ie. websites on the internet) that appear to tell people that the very last 'bin' or frequency point in a FFT plot is exactly associated with the frequency 'fs' (the sampling frequency).

The right-most point in an FFT plot usually represents a frequency of [(N-1)/N] * fs.

N is the number of time domain sampling points. However though, for relatively large 'N', that last frequency is *almost* the same as "fs".

The gap (frequency resolution) between adjacent frequency points (ie. between two bin frequencies) is equal to fs/N.

So.... if we have N = 100 time domain sample points, then the FFT magnitude plot has 0 to 99 frequency points (ie. still a total of 100 points). Point number [ 0 ] represents 0 Hz (ie. DC). Point number [50] represents a frequency of 5 * gap = 50*fs/100 = fs/2 (ie. half the sampling frequency).

The entire FFT MAGNITUDE plot will look symmetrical about point [50]. Normally, ignore the stuff above the half-way point, ie. point [50]. So, when discussing the magnitude spectrum, bin [ 0 ] to bin [50] are generally the bins (or frequency points) of interest, which represents 0 Hz up to fs/2, with frequency gaps of fs/N between adjacent points.