Did you lose your blog and is it hosted? If so, your host should have the backups available to restore your blog. If you want to restore the blog yourself, you need to restore both the blog software and database. If you have the database structure and data, then execute the .sql script to restore database and upload the blog software. You may need to change database configuration information, if you need help with specific details just let me know.
If it is MySQL database then you can not simply upload it like FTP. You will need to restore it. If you have PHPMyAdmin then you can restore it from there or you may provide your backup copy to your hosting provider to restore it on your behalf. If you create the same database as mention in your blog config file then probably you do not need to make changes.
i have uploaded the wordpress database backup plugin.through this plugin i am going to download backups.is it right thing to do?
I have not used this plugin but I think should work properly. Also you can take the backup from the control panel if you have cPanel. Also in wordpress, you just need to define database name, database username and password to connect to your db. So if you move your blog to other location then restore your MySQL database then make the required change in wp-config.php file.