Les Galeries Lafayette is one of the big Parisian department stores. It's so big there it has several buildings. There are smaller branches in the suburbs and other cities in France. Other big department stores are Le Printemps (almost next door to Galeries Lafayette) and B.H.V. On the left bank, there is Au Bon Marché.

The main Galeries Lafayette store is on Boulevard Haussmann, just behind the (old) Opera. If you are taking the metro, the Chaussée d'Antin station is the closest, but Opera and Havre Caumartin are not far. The RER station, Auber, is also very near.
le galeries Lafayette are a large department store in Paris - (and in other French towns as well)