you definatley need to read BOL, however i guess you must be beginner so if you dont want to get confused with syntax in bol, refer the below code
backup database test_database to disk = 'D:\test_database.bak'
test_database is the name of the database.
'D:\test_database.bak' is the location on server where the backup file will be created.
This is the vanila code to do full database backup.