1. Backup database:
#mysqldump -u username -p[username_password] databasename > /path_to_your_db/databasename_backup.sql

For example: if you backup database with user is root and pass is yourpassword and have the path to your database is /home/username_of_account/public_html/backup_folder/

#mysqldump -u root -pyourpassword databasename> /home/username_of_account/public_html/backup_folder/Your_DB_backup.sql

2. Restore database:
#mysql -u username -p[username_password] databasename < /path_to_your_db/databasename_backup.sql

For example: you want to restore database with user is root and pass is yourpassword then using this command -
mysql -u root -p yourpassword databasename < /home/username_of_account/public_html/backup_folder/Your_DB_backup.sql