How do we know that whatever permissions given to a DATABASE/OBJECT/USER ?

This script lists the permissions granted to the Current Database:  
SELECT permission_name 'DB Permission Lists'  FROM FN_MY_PERMISSIONS(NULL, 'DATABASE')  
ORDER BY subentity_name, permission_name

This script lists the permissions granted to an Object  
SELECT Entity_Name,permission_name 'Permission Lists' FROM FN_MY_PERMISSIONS('ObjectName', 'OBJECT') 
WHERE SUBENTITY_NAME ='' ORDER BY subentity_name, permission_name ; 

This script lists the permissions granted to an User  
SELECT Entity_Name,permission_name 'Permission Lists' FROM FN_MY_PERMISSIONS('UserName', 'USER') 
ORDER BY subentity_name, permission_name ;