The is below is correct,if a little oxford. Basicly yeast is added to the "container" so that the beer continues to be live ie improve with age. Two basic types;
cask and bottle conditioned.
Cask will see a hand pull/pump used for dispence rather than a font,bottle condioned will need careful lable reading to identify if you dont know the brand.although there is now a "
CAMRA says this real ale" labling scheme starting to appear,to help
the uninitiated.