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
   - SYSTEM BYPASS!!!

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 ?