I'm new in speech-processing and there are some notions confused me.

Through Fourier Transform, we can get spectra of specific sound signals, the harmonic frequencies can be shown as the peaks in the spectrum. So are those harmonic frequencis i.e. the peak frequencies equivalent to the formant frequencies? Or what's the relationship between harmonic frequencies and formant frequencies?

BTW, I have anothor question, that is, why the harmonic frequencies are integer multiples of the fundamental frequency? What if I synthesize a sound with a 440Hz wave and a 441Hz wave? Will the fundamental frequency of that sound be 1Hz!?