CST in frequency domain

Can someone explain me more how to use the frequency domain solver?
I don't understand very well what means: 'solves the problem for every frequency separtely'.
Then there is something else: 'this FD use a special broadband frequency sweep technique in order to derive the full broadband spectrum from a relatively small number of frequency samples'?
Actually, I want to see the electric field distribution in a simple cylinder of dispersive material (water). To use the frequency domain solver I have to define a waveguideport. Can someone give an advice? How shoud I define this waveguide port?
thx

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