Filtration of rectangular pulses

Hallo, I have a problem with this task and I need help.I can't understand how to filter these signal and how to compare it with the original sgnal.If anyone can help me to resolve this task i will be very thankfull.

''Generate a periodic rectangular signal with amplitude of 0.5, mean of 0.5 and period of 0.02 s. Filter this signal with a Low pass filter with cutoff frequency of 300 Hz. Plot the spectra of the original and the filtered signal and compare the plots of both signals in the time domain.''

[Image Analyst]

Did you try searching the forum for words like pulse train or square wave or cutoff filter?

http://www.mathworks.com/matlabcentral/answers/8626-how-do-i-get-help-on-homework-questions-on-matlab-answers