matlab - how to do DFT on different functions in time and frequency domain? -

i beginner @ fft , trying learn fft in matlab. have problem concept of fft , difference of time , frequency domain. have 2 questions , grateful if me learn them.

1- dft can implemented both in time , frequency domain??? difference between sampling in time , frequency domain???

2- want dft on step function ( t=45 seconds , sampling interval in time domain given 0.01 s) can me how write code in matlab ????

thanks,

1.a dft transistion time domain frequency domain , and idft opposite (f->t). sampling in time means @ signal in time intervals (e.g. 0,001s). in frequency domain tells how frequency between each value. last value in frequency domain inverse of sample time (in example above 1000hz). if dft 1000 samples spacing of 1hz.

2. just instert 45s/0.01s samples dft. make sure 1 period of function, else window leakage.