Frank is right as a beginner to be confused.  Here in the UK the most popular
hive is the National which has bottom bee space instead of top as Frank
describes.  However many people recognise that top is more efficient and
modify their hives or, if they build their own, make them with top space.
They also buy second hand equipment which, of course doesn't quite match
their own.  Inevitably the equipment gets mixed with predictable results.

I once inherited an apiary of home made CDB hives (an obsolete Irish design).
 The chap who made them was a craftsman. Everything fitted. Nothing was stuck
with propolis or burr comb.  They were and are a joy to work with and the
bees love them.

Chris