Help with FFT mode

I better explain fft output to you than answer your figures which are not clear to me:

N points fft output means N bins covering frequencies of +/- sampling frequency/2, (and usually indexed as 0 ~ N-1)

approximately:

bins 0~N/2 represent frequency range 0 ~ Fs/2 (Fs = sampling frequency sample/sec)

bins N/2+1 ~ N-1 represent frequency range -Fs/2 ~ 0

thus dc is at start and end(wrap up)

If your signal is real only then both halves get equal (mirror)

thus frequency of spectrum at point n: f(n) = Fs * n/N in Hz and its amplitude or phase is the value of amplitude or phase at n

amplitude = sqrt(Re^2 + Im^2) as you know

If you require fft results then use some simple vector e.g. constant, tell me your resolution and I will get you the result.