Quicken stores all data for a set of accounts and transactions in a single data file. Multiple data files can be used if you want to keep accounts separate, for example, for separate finances within the same family; however, combined finances should usually be kept in the same file.
Quicken Data Files
Quicken data files are stored in a default location depending upon your version of Quicken. You can open recently used files with the Open Recent... command on the File menu with any Quicken version. Otherwise, look for your Quicken files in:
C:\Documents and Settings\User Name\My Documents\Quicken
on Windows, and in the Quicken folder in your Documents folder on a Mac.
Other Quicken Files
Quicken may store other files in the folder alongside your data, including files containing images and backup files associated with your data. Your original data file will have an extension of QDF.