Example of Observer usage in config.xml file

config.xml

<?xml version="1.0"?>
<config>
	<global>
		<events>
			<customer_register_success>
				<observers>
					<example_customer_register_success>
						<type>singleton</type>
						<class>module/observer</class>
						<method>customerRegisterSuccess</method>
					</example_customer_register_success>
				</observers>		
			</customer_register_success>
		</events>
	</global>
</config>