The literal translation of Grundgesetz is Basic or Fundamental Law: the choice of name reflecting its origin in the post Second World War political landscape of a divided Germany.
However, the re-unification of Germany did not lead to the drafting of a new constitution (Verfassung) as the Grundgesetz (GG) had proved its worth over time.
The Grundgesetz is the supreme norm in the German legal system: see Articles 1 III and 20 III GG.
Official abbreviation is GG
The first division is the Artikel. An Artikel is often made up of paragraphs Absatz or Abs., and paragraphs of clauses Satz or S.
Some English language commentary and analysis. Remember also to check for articles (in all languages!) in law journals via IFLP, ILP etc
The Constitution of Germany by 
German Constitutional Law: Introduction, Cases, and Principles by 
Tradition and Transformations : the rise of German constitutionalism by 
Debates in German Public Law by German Constitutional History
Be prepared to see that SOLO searches uncover useful titles held by other parts of the Bodleian
From Empire to Union: conceptions of German constitutional law since 1871 by 
The German Federal Constitutional Court : the court without limits by The file references in citations reveal the type of application - about which follow the first link below
BvB Party-Ban Proceedings
BvC Electoral Complaints
BvE Organstreit Proceedings against Constitutional Organs
BvF Abstract Judicial Review of Statutes
BvL Specific Judicial Review of Statutes
BvM Review of Public International Law as Part of Federal Law
BvQ Preliminary Injunctions
BvR Constitutional Complaints
PBvU Plenary decision
Vz Verzögerungsbeschwerde Delay appeal