The difference between a lager and an ale really comes down to the yeast used. An ale yeast is a top fermenting yeast that can ferment at higher temperatures and is a faster process. A lager yeast is a bottom fermenting yeast that requires colder temperatures and a longer process.
The word lager comes from the German word Lagern, which means to store, to hold or store. And really that's whats required to make a lager as it takes a long time for the sugar to ferment out into alcohol using a lager yeast. So they tend to actually be very difficult beers to make. Whereas with an ale its a faster process, also the ale yeast tend to produce some esters which provide flavorful components on their own.
And a lager yeast is very clean so you get very few flavor components from the lager yeast. So essentially the lager is a much harder beer to make, there's nowhere for off flavors to hide, you really are only getting the ingredients in there. Whereas with an ale you might find quite a few different flavors that you know will help make that beer, you know very flavorful delicious experience, and one of the most unfair parts of the brewing world, many more people prefer ales to lagers even though it takes more skill and precision in my opinion, to make a lager. So again, the difference between a lager and an ale is the type of yeast used.