ij is the command line tool for controlling the Derby database. It should be in your path so you can use it while in any directory. To start ij from a command prompt or terminal type
C:\> ij or ~ $ ij
This assumes that ij or ij.bat is in the PATH.
ij> connect 'jdbc:derby:logindb:create=true;'
ij> connect 'jdbc:derby:logindb;'
With an Embedded database, two db clients cannot be in the database at the same time. This can lead to some pretty uninformative errors.