A Bundesland is a part of Germany, as you may compare it to States in the USA, they have some major differences. They only have limited powers over certain topics, for example education. There are nation-wide guidelines but the exact execution is based in the Bundesland.
If it would work this should be a pretty clever concept of
federalism: Things which have to be done nation-wide should be done on the national level (criminal law, general guidelines). But as most democratic concepts this does not work perfect. The Bundesländer try to support their own region most. So it comes to differences between the Bundesländer, but also between the national level (
Bundestag) and the nation-wide representation of the Bundesländer, the
Bundesrat. The Bundestag sometimes tries to lower its costs on the back of the Bundesländer.
Ok now some infos on the Bundesländer themself:
There are 16 Bundesländer