In the Roles,

when I assign the permission for each object, I don't understand what is Exec & DRI?

What is it?

Here is an extract taken from the sql server helpfile, this will answer your question....

Object Properties (Permissions Tab)
Use this tab to view or specify the following options.

Options
Object

Specify the name of the object.

List all users/user-defined database roles/public

List all users and database roles for the selected database. Click the appropriate box to modify object permissions.

List only users/user-defined database roles/public with permissions on this object

List only users or database roles that already have permissions on the object. Click the appropriate box to modify database user permissions.

User/Database roles/public

View the user ID or database role.

SELECT

Grant, revoke, or deny SELECT permissions on this object.

INSERT

Grant, revoke, or deny INSERT permissions on this object.

UPDATE

Grant, revoke, or deny UPDATE permissions on this object.

DELETE

Grant, revoke, or deny DELETE permissions on this object.

EXEC

Grant, revoke, or deny EXECUTE permissions on this object.

DRI

Grant, revoke, or deny declarative referential integrity permissions on this object.

Columns

Display the Column Permissions dialog box, where you can manage permissions for each column.