Their basic difference is measured in IBU (International Bittering Units) being the international betterness measuring unit of beer and results from the amount of hops used in their production. For the hard-core beer fans, bitterness in a beer is considered essential. 
The hops participate within the aroma and the body and clearly gives a beer character. It's like the salt and pepper. 

The term “lager” technically indicates a low fermentation beer where the yeast settles at the bottom. However low fermentation beers, also include “pilsener” or simply “pils” beers which descend from the famous town Bohemia that categorise beers with a strong aroma with a hops taste and with a higher IBU from the rest of the laggers.

In order to enjoy them properly, serve both at temperatures from 4 to 7 degrees C without ice nor iced glasses as ice alters the beer's characteristics. The glass must also be sparkling clean as the foam's quality and durability depends on that. At a table lagers accompany almost everything since they love appetizers, while pilsners are prefered with small and spicy dishes containing olives , spices, endives or even spicy cheeses like kefalotyri.