Ales are fermented warmer- generally in the 60s, and have much more yeast character.
Lagers are fermented at 48-53 degrees and are "clean" and crisp. They also undergo a lagering time- generally near freezing for 6 weeks or so- before bottling.
Lagers are considered advanced brewing, due to the size of the starter needed, the need for ultra strict fermentation temperature control at about 50 degrees and then the lagering period.