Code Access security

In visual studio
http://blog.mastykarz.nl/code-access-security-policy-template-visual-studio-2010-sharepoint-developer-tools/

In web.config file
http://blogs.msdn.com/b/navdeepm/archive/2009/09/19/code-access-security-in-sharepoint.aspx

Using C#
http://msdn.microsoft.com/en-us/library/system.security.permissionset(v=vs.110).aspx

Config tool
http://msdn.microsoft.com/en-us/library/xbk2s3fa(v=vs.90).aspx