Can I decide what categories show on my posts page?

$args = array(
    //post basics
    'post_status'    => 'publish',
    'post_type'      => 'post',
    'posts_per_page' => 10
    //order
    'orderby'        => 'date',
    'order'          => 'desc',
    //category query
    'tax_query'      => array(
        array(
            'taxonomy' => 'category',
            'field'    => 'slug',
            'terms'    => 'news' //make this the slug of the category you want to use
        )
    )
);
$posts = new WP_Query( $args );

$posts will now contain 10 posts from news. You can tweak this as you see fit, it’s pretty simple to do, and WP_Query is INCREDIBLY powerful.

Docs: WP_Query