i have as a homework to do a desktop aplication using C#,it will be good if i use also and databases,plsss could anyone give me some ideas what willl be good to work on...(sorry for my english)...

Create a simple bank manage system or liblary, you will use DB :)

A tree with possible choise's

+ Client
   - Add
   - Find (Show all in list and you for each you have some actions up in a menustrip (edit/delete/etc...)
   - Movements
+ Bank
   - Clients
   - Company
   - Find Client
   - Block Client Account
   - ATM 
+ ATM Manager
   - Disable
   - Watch Exchanges
   - Options 
+ System
   - Administrator
   - Create New User
   - Change Password
   - Delete User
   - Options
+ Employers
   - Add
   - Find
   - Payments
+ System LOG
   - General
   - Warning

Don't wait, just start your work. Learn SQL queries and run them via ADO.NET class library.

Perhaps do something related to what you've been LEARNING ALL YEAR.

start with a calculator application, you ll learn more about the datatypes like int and float.
then go with a simple application which will use a DB. may be u can use a student record maintenance, insert, update or delete a student record, something like that.

Library system, it's been done to death but it's a winner every time !

What are you using for your database, MS Access, SQL Server, Orical ?