I have been plotting and scaling some spectra for a data series that I obtained by applying Fourier Transform, I wish to construct a signal that looks like the original using the frequences. The graph shows that there is a frequency with zero frequency and amplitude $0.337007596$, which doesn't make sense to me. Reading on the internet I've come to understand that this is the "DC value," but I'm not sure how to interpret it, any help would be appreciated.
Something else that I dont understand is that the 0-frequency component has the greatest amplitude.
The Fourier transform of a signal $v(t)$ is
$$V(f)=\int_{-\infty}^{\infty} v(t)e^{-j2\pi ft}\;\mathrm{d}t$$
If you just substitute $f=0$ in the above equation, you obtain
$$V(0)=\int_{-\infty}^{\infty} v(t)\;\mathrm{d}t$$
which is just a scaled version of the mean of the signal. Any nonzero-mean signal will have a zero-frequency component in its Fourier transform.