If you want manipulate the data of a CRM 2011 instance is necessary to follow some rules.
For CRUD and business operations you need use the CRM 2011 web services (also in combination with LINQ)
Is also possible (if you can connect to the DB) to read the data from Filtered Views, a Filtered View is a view mapped on a standard CRM entity (for example to read the data from the entity Account you can use the view FilteredAccount)
Read or modify the data directly from the tables is not supported.
If you want to know the structure of the entities you can use the Customization area inside CRM, or install the Metadata Browser (a solution available inside the CRM 2011 SDK) to see the attributes and the relationships.
A good starting point is always the CRM 2011 SDK, you can download here:
http://www.microsoft.com/en-us/download/details.aspx?id=24004
Inside you will find many examples (if you want to use LINQ check the early-bound ones) and the assemblies and tools for development.