How to: Create a page to display post list under a specified category

1: Go to WP Administrate control panel -> Designe -> Theme Editor;
2: Open "Main Index Template (index.php)", copy its all content;
3: Open local text editor such as Notepad, paste copied content into text editor new file, save as your new WP page file name such as MyList.php;
4: At the top of this php file, add the following code:
<?php
/*
Template Name: MyListPage
*/
?>

"MyListPage" will be your page template name which is for your selection later when you create a new page;
5: Find "<?php if (have_posts()) : ?>";
Above this line, Add "<?php query_posts(‘showposts=20&cat=18’); ?>";
cat=18 is your specified category ID
6: FTP this php file to your remote hosting "/wp-content/themes/YOUR CURRENT THEME FOLDER NAME/;
7: Write a new page in WP, give a Title like "MyList", select page template to MyListPage, just save it;
8: Done; go to see your new page "MyList".