Aquarium Filter system and filter media

Do you need to understand this in order to choose which filter system is suitable for your requirement ? ....Yes.
But the good news is when you buy your aquarium most already have paired with a filter system and the seller would probably ask some question in order to understand your requirement....so tell him/her what type of set up your planning ,type of fish ,quantity of fish and your budget so that he/she can pair accordingly . This is what most aquarist  miss out : How does your aquarium eco system works , well actually to keep the aquarium healthy you got to have a good Nitrogen cycle  

This diagram shows the nitrogen cycle, ammonia, nitrite and nitrate is toxic to fishes as it will encourage disease in the fish. Bacteria in the aquarium will eat up the ammonia and nitrite ,this process the will produce the dreaded nitrate. If nitrate level breach 50 ppm some fish will start to get sick and may die due to the sickness . Here is were your filtering system plays it's role by keeping the nitrate in the filter media so that your aquarium nitrate level is in check.
* For new tank prior to set up it is recommended to add bacteria to your tank, this is to encourage the     Nitrogen cycle to start.

Now here a few sample of available filters :

Tips : the larger your filter the more nitrate it will hold and this prolong the cleaning schedule so it also depend how frequent you perform your tank maintenance 
Size of filter :
 Filter size of about 30% of your aquarium or pond is the most suitable size and require lesser attention , frequency of maintenance 1~3 years ( for indoors recommended yearly due to fishy smell as for outdoor can opt for longer period ) although the maintenance period is longer but the cleaning of filter system is a real dirty job so be prepare.
If your location cannot fit such a big filter , a smaller ones will do also the only thing is have to clean more often. Example change partial water every 2 weeks and clean the filter media or replace with new one .
Tip to prolong cleaning schedule : feed less food, cleaning tank of waste and may try to keep a few life plants .
Or you may also use O3 ionizer to enrich the oxygen  level or use additional filter media ie :zeolite or carbon ( charcoal )
Hope this info be useful to you .