Magento – how to create section and tabs in admin panel

The default values must be added in the config.xml file.
Add this inside the <config> tag:

<default>
   <testtabsection><!-- tag of the system.xml section -->
        <grouptestgroup><!-- tag of the system.xml group -->
            <fieldtestfield>Your value here</fieldtestfield><!-- tag of the system.xml field -->
        </grouptestgroup>
   </testtabsection>
</default>

Clear the cache and check your system configuration section.

Magento core has all the example you need. Look at how the salesrules adminhtml is built. It is a good example of how tabs can be built using layout.xml

You just need to systematically duplicate the structure into your own module, and you will have tabs, handled by layout.xml. It is then easy to add tabs as needed.

Here is a rundown:

Have a look at promo.xml in app/design/adminhtml/default/default/layout/promo.xml, specifically at the handle <adminhtml_promo_quote_edit>

Here you will find the layout that defines the tabs used in the promo rule section:

<reference name="left">
    <block type="adminhtml/promo_quote_edit_tabs" name="promo_quote_edit_tabs">
        <block type="adminhtml/promo_quote_edit_tab_main" name="promo_quote_edit_tab_main" />
        <block type="adminhtml/promo_quote_edit_tab_conditions" name="promo_quote_edit_tab_conditions"/>
        <block type="adminhtml/promo_quote_edit_tab_actions" name="promo_quote_edit_tab_actions"/>
        <block type="adminhtml/promo_quote_edit_tab_labels" name="promo_quote_edit_tab_labels"/>
        <block type="adminhtml/promo_quote_edit_tab_coupons" name="promo_quote_edit_tab_coupons">
            <block type="adminhtml/promo_quote_edit_tab_coupons_form" name="promo_quote_edit_tab_coupons_form"/>
            <block type="adminhtml/promo_quote_edit_tab_coupons_grid" name="promo_quote_edit_tab_coupons_grid"/>
        </block>
        <action method="addTab"><name>main_section</name><block>promo_quote_edit_tab_main</block></action>
        <action method="addTab"><name>conditions_section</name><block>promo_quote_edit_tab_conditions</block></action>
        <action method="addTab"><name>actions_section</name><block>promo_quote_edit_tab_actions</block></action>
        <action method="addTab"><name>labels_section</name><block>promo_quote_edit_tab_labels</block></action>
        <action method="addTab"><name>coupons_section</name><block>promo_quote_edit_tab_coupons</block></action>
    </block>
    <block type="adminhtml/template" template="promo/salesrulejs.phtml" name="promo_quote_edit_jsinit"/>
</reference>

So, from the above you will find that you first define the main tabs container block:

<block type="adminhtml/promo_quote_edit_tabs" name="promo_quote_edit_tabs">

The block class definition is as such:

class Mage_Adminhtml_Block_Promo_Quote_Edit_Tabs extends Mage_Adminhtml_Block_Widget_Tabs

which gives you the 'addTabs' functionality, as used in the layouts.

This is thus your starting point.

Next you define a block that will become a tab within this container.

In the example, the first block is <block type="adminhtml/promo_quote_edit_tab_main" name="promo_quote_edit_tab_main" />

and the class is defined as:

class Mage_Adminhtml_Block_Promo_Quote_Edit_Tab_Main
    extends Mage_Adminhtml_Block_Widget_Form
    implements Mage_Adminhtml_Block_Widget_Tab_Interface

You then attach this block to the container using the addTab action

<action method="addTab"><name>main_section</name><block>promo_quote_edit_tab_main</block></action>

and repeat the process for each tab you add.

The coupons tab gives you a good example of how to place a grid within a tab.

I hope this pointer gets you in the right direction.

Ask for any further clarification.