A lager is fermented at cooler temps than an ale, usually around 50-55. Because of this it takes a little longer for a lager to get done fermenting. Also, lager fermentations are a little trickier than regular ale fermentations because. Yeasts are finicky at cooler temps, and need to stay at a very constant temp to not quite the job early. Since fermentation is an exothermic reaction, this means monitoring the beer temp, and not the ambient temp to keep it steady.
Also, sometimes lager fermentations need a diacetyl rest before the lagering phase begins. This involves raising the temp to ale temperatures for a period of 24 or so hours when there is only a few points left before FG is reached. Good yeast handling practices can often eliminate the need for a D-rest.
Lagers tend to be more delicate beers also, so more care need to be taked to insure no off flavors will be produced anywhere, because there is nothing for off flavors to hide behind.
That said, schwarzbier is one of my favorite styles of beer, I highly recommend brewing one. I have an award winning recipe posted in the database (and in my recipe dropdown).