Please help me understand laplace transforms.?

Can someone shed some light on what you are doing when you take the laplace transform of an equation? I understand the fourier series and that it is a special case of the laplace transform when sigma is equal to zero. However, when taking the fourier series of a function you can plug in different harmonic values to solve for the magnitudes of the frequency, how does that parralell to the laplace transform? Can you extract frequencies from a laplace transform like a fourier transform? Would you ever plug in harmonic values and values for sigma and solve? What vales does sigma represent? What does 'complex frequency' refer to? Since a fourier series can have sin and cos components, seperated by a phase angle of ninety degrees, is a solution considered a 'complex frequency'?