How do I remove Categories and Archives and more..

By editing your theme’s sidebar.php template file and removing <?php wp_list_categories();?> and <?php wp_get_archives();?>.

To remove the Site Description “Just Another WordPress Site” from the header, remove the following code from the header (probably in a “header.php” file):
<?php bloginfo('description'); ?>
OR
`<?php echo get_bloginfo(‘description’); ?>

To remove the default sidebar content, go to your wp-admin, navigate to “Appearance -> Widgets”.

Then, either remove the undesired Widgets, or, if no Widgets are configured, add the ones you want to display in the sidebar.

If you want the sidebar to appear, but with nothing in it, remove the default content in “sidebar.php”.

If you don’t want the sidebar to appear at all, remove the following from your template files:
<?php get_sidebar(); ?>
You will need to look in “index.php”, “single.php”, “page.php”, and perhaps others, e.g. “archive.php”.