find your mysql location where you installed
C:\Program Files\MySQL\MySQL Server 5.0>
then move to bin folder
C:\Program Files\MySQL\MySQL Server 5.0\bin>
then use this comand
mysql --user=root -proot testdb > export.sql
this will create export.sql file in the bin folder.
if you want to save backup file in the specific path then you give like that
mysql --user=root -proot testdb > d:\db_backup\export.sql
C:\Program Files\MySQL\MySQL Server 5.0>
then move to bin folder
C:\Program Files\MySQL\MySQL Server 5.0\bin>
then use this comand
mysql --user=root -proot testdb > export.sql
this will create export.sql file in the bin folder.
if you want to save backup file in the specific path then you give like that
mysql --user=root -proot testdb > d:\db_backup\export.sql