need sa password set by Web PI for gallery app install

I am a newbie just trying to get up and running in .net

I installed VS2012 Express via Web PI.  The "packages" seem to also include many versions of SQL Server:

SQL Server Express 2008 R2 SP2
Microsoft SQL Server Compact 4.0 SP1
Microsoft SQL Express LocalDB Edition 11.0

When I try to install a sample app from the Web Gallery, it asks for the sa password for SQL Server.  I never set it and don't know how to.  I sure would be grateful for a push off the diving board into the deep end.

Thanks!