To add to steve's comments, there is physically no difference between lager and beer, they are both made with the same basic ingredients, water malt hops and Yeast, it is the yeasts that make the final beer, Lager is basically a broad style of beer.
Ale is actually a term for unhopped beer, a term used before hops were widely used in beer making, beer was used to distingish between a hopped beer and an unhopped drink (ale)
Lager yeasts tend to be of the bottom fermenting variety, I.e they work from the bottom of the beer, (not strictly true as plenty are suspended in the wort whilst fermentation is going on, however they drop out of suspension when fermentation is comnplete, lager yeasts tend to work at lower temps too, (you don't get a very clean beer when fermenting a true lager yeast at ale temperatures)
ale yeasts tend to be top fermenting, ie lots of them form a skin on top of the beer when fermenting and shortly after they have done their job (burton ale is a classic example as are the yorkshire strains) they don't work very well sub 15 deg C where lager yeasts thrive.
Unless you can control your fermentation temperatures, such as in a fridge with your own PID controlling temp, don't try a lager, it will be gash, also if you buy a lager kit the chances are the yeast that comes with it will be a clean fermenting ale yeast, therefore you will not be brewing a true lager.
To sum up Lager means "TO STORE" nothing more its just a type of Beer.
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