Sump Help

I am totally clueless when it comes to sumps but i would really like to set 1 up. I have no idea at all how to make 1 so i have some questions. What do u put in a sump?? How do u make 1? Can i put a piece of acrylic in it to make a sump and a fuge? Would a 20 gallon be sufficient for a 55 gallon? THANX
 
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