Well, you don't specify what exactly you're seeing that's different... but I'll take a stab at a common problem. The result of an FFT has the DC frequency (i.e. 0) in the first bin, proceeded by the real frequency spectral bins, then proceeded by the negative spectral bins. Use a "shift" function to shift the zero bin to the middle and re-arrange the negative components to be left of zero for plotting:
fftshift - Rearranges the fft output, moving the zero frequency to the center of the spectrum[
^]
The spacing of the spectral bins is essentially Fs/N, where Fs is the sampling frequency and N is the FFT size. The larger the FFT size, the tighter your bin spacing for a given sample rate (i.e. you get more frequency resolution). Due to computational complexity, typically N will be a power of 2... if you feed less samples than a power of 2 to an FFT library, they'll zero pad up to the closest power of 2.
As for the magnitude scaling of your graph, well... there's a handful of scaling options but 1/N and 1/sqrt(N) are common options.
Good luck!