How to set number of columns on product listing page?

<?php $_columnCount = $this->getColumnCount(); ?>

              and replace it with:

<?php $_columnCount = 4; ?>

How to create module in magento?

app/etc/modules/Custom_Manufacturerlogo.xml

app/code/local/Custom/Manufacturerlogo/Block/Manufacturerlogo.php

app/code/local/Custom/Manufacturerlogo/controllers/IndexController.php

app/code/local/Custom/Manufacturerlogo/etc/config.xml

app/code/local/Custom/Manufacturerlogo/Model/Manufacturerlogo.php

app/code/local/Custom/Manufacturerlogo/Model/Mysql4/Manufacturerlogo.php

app/code/local/Custom/Manufacturerlogo/Model/Mysql4/Manufacturerlogo/Collection.php

app/code/local/Custom/Manufacturerlogo/Model/Status.php

app/code/local/Custom/Manufacturerlogo/sql/manufacturerlogo_setup/mysql4-install-0.1.0.php

app/design/frontend/default/default/layout/manufacturerlogo.xml

app/design/frontend/default/default/template/manufacturerlogo/manufacturerlogo.phtml

app/code/local/Custom/Manufacturerlogo/Block/Adminhtml/Manufacturerlogo.php

app/code/local/Custom/Manufacturerlogo/Block/Adminhtml/Manufacturerlogo/Edit.php

app/code/local/Custom/Manufacturerlogo/Block/Adminhtml/Manufacturerlogo/Grid.php

app/code/local/Custom/Manufacturerlogo/Block/Adminhtml/Manufacturerlogo/Edit/Form.php

app/code/local/Custom/Manufacturerlogo/Block/Adminhtml/Manufacturerlogo/Edit/Tabs.php

app/code/local/Custom/Manufacturerlogo/Block/Adminhtml/Manufacturerlogo/Edit/Tab/Form.php

app/code/local/Custom/Manufacturerlogo/controllers/Adminhtml/ManufacturerlogoController.php

app/code/local/Custom/Manufacturerlogo/Helper/Data.php

app/design/adminhtml/default/default/layout/manufacturerlogo.xml

Sample valid credit card numbers for testing

Here is a list of sample/dummy/test credit card numbers, which are safe to use when you test credit card functionality on a website or application that involves credit card transactions. These credit card numbers validate properly but they are not actually in use.

American Express:

378282246310005
3111111111111117
343434343434343
370000000000002
340000000000009
371449635398431
378734493671000

Visa:

4111111111111111
4007000000027
4222222222222
4012888888881881

MasterCard:

5105105105105100
5111111111111118
5454545454545454
5500000000000004
5555555555551111
5555555555554444

Discover:

6011111111111117
6011000000000004
6011000990139424
6011601160116611
6111111111111116

Hope this helps. Thanks.