Step 1: Create New Template

Create a new template file in the following directory (you may want to simply copy an existing template, such as 1column.phtml) and name it with an appropriate name (ie: home.phtml if that template will be used for your home page).

app/design/frontend/YOUR_INTERFACE/YOUR_THEME/template/page/

whereas YOUR_INTERFACE typically remains "default" and YOUR_THEME can also be "default" (please see Design-Guide about proper naming of themes and interfaces)

Step 2: Create a new module

In order to customize the configuration of Magento without hacking into existing files we need to create a new module. This is very simple. The module will only contain a configuration file that updates the section that lists the available templates for the CMS.

We'll call the module Banana (just a example) and its package name Fruit (also just an example).

Note: You may (and probably should) choose a different module/package name, just be consistent throughout the process.

We need to tell Magento about our new module, so create a new file:

app/etc/modules/Fruit_Banana.xml

with the following content:

<?xml version="1.0"?>

<config>

<modules>

<Fruit_Banana>

<active>true</active>

<codePool>local</codePool>

<depends>

<Mage_Page />

</depends>

</Fruit_Banana>

</modules>

</config>

Now we need to actually create the module itself. Create the following file (and the neccessary folder structure):

app/code/local/Fruit/Banana/etc/config.xml

with the following content:

<?xml version="1.0"?>

<config>

<modules>

<Fruit_Banana>

<version>0.1.0</version>

</Fruit_Banana>

</modules>

<global>

<page>

<layouts>

<INTERNAL_NAME_FOR_YOUR_NEW_LAYOUT translate="label">

<label>LAYOUT_NAME</label>

<template>page/LAYOUT_FILE_NAME.phtml</template>

<layout_handle>LAYOUT_HANDLE</layout_handle>

</INTERNAL_NAME_FOR_YOUR_NEW_LAYOUT>

<!-- add more layouts here -->

</layouts>

</page>

</global>

</config>

The capitalized parts need to be filled in by you.

Any new layouts you want to add should to be in the following format:

<layout_description translate="label">

<label>Layout Name</label>

<template>page/template_name.phtml</template>

<!-- defining the layout handle is optional -->

</layout_description>

Using the same steps, and modifying them for each template, you can create new layout templates for use on any CMSpage.

You're done!

Also, take a look at the config.xml of the Page module in the Mage package; it defines the layouts that come with Magento:

app/code/core/Mage/Page/etc/config.xml

On line ~47(version 1.5.1.0) find:

<page>

<layouts>

<empty module="page" translate="label">

<label>Empty</label>

<template>page/empty.phtml</template>

<layout_handle>page_empty</layout_handle>

</empty>

<one_column module="page" translate="label">

<label>1 column</label>

<template>page/1column.phtml</template>

<layout_handle>page_one_column</layout_handle>

<is_default>1</is_default>

</one_column>

<two_columns_left module="page" translate="label">

<label>2 columns with left bar</label>

<template>page/2columns-left.phtml</template>

<layout_handle>page_two_columns_left</layout_handle>

</two_columns_left>

<two_columns_right module="page" translate="label">

<label>2 columns with right bar</label>

<template>page/2columns-right.phtml</template>

<layout_handle>page_two_columns_right</layout_handle>

</two_columns_right>

<three_columns module="page" translate="label">

<label>3 columns</label>

<template>page/3columns.phtml</template>

<layout_handle>page_three_columns</layout_handle>

</three_columns>

</layouts>

</page>

If you don't care for updating Magento and love hacking core files (something you generally shouldn't do, unless you know what you're doing) you can also just update this file (app/code/core/Mage/Page/etc/config.xml). Beware though that Magento updates can override the changes you've made.

From magentocommerce -  Themes and template customization - Magento