let me explain magento blocks in details hope it will help you to understand complete block mechanism
Everything in magento is a module , so all the modules have their controllers which are used for url routing system . lets take an example of url e.g http://example.com/index.php/customer/account/index/
module routes in this way module_controller_action
as you can see here module is customer , controller is accountcontroller and action is indexaction (all magento controller action works in this manner e,g editAction = edit on URL deleteAction = delete). You can verify by visiting this path /app/code/core/Mage/Customer/controllers
also related xml can be found under /app/design/frontend/base/default/layout customer.xml
Magento Reference Block
Now its time to explain reference block as its name suggests reference block is help ful to give a reference to your block . Suppose you want to integrate your block in left postion of the store then you can easily call
<reference name="left">
<block type="core/template" after="-"
name="sleek" template ="Sleekaccordian/new.phtml" /></reference>
Reference Action Method
Under reference tag we can call functions as well using action method as per the given example for newsletter.xml
<reference name="customer_account_navigation">
<action method="addLink" translate="label" module="newsletter">
<name>newsletter</name><path>newsletter/manage/</path>
<label>Newsletter Subscriptions</label></action>
</reference>
this reference (customer_account_navigation) is defined under customer.xml
<block type="customer/account_navigation" name="customer_account_navigation"
before="-" template="customer/account/navigation.phtml">
<action method="addLink" translate="label" module="customer">
<name>account</name><path>customer/account/</path><label>Account Dashboard</label></action>
<action method="addLink" translate="label" module="customer">
<name>account_edit</name><path>customer/account/edit/</path>
<label>Account Information</label></action>
<action method="addLink" translate="label" module="customer">
<name>address_book</name><path>customer/address/</path><label>Address Book</label></action>
</block>
now as per the block class if you’ll visit
/app/code/core/Mage/Customer/Block/Account then you’ll find addLink function under Navigation.php