showing posts only in category not on ‘front page’

Actually you control how many posts are displayed on the main page with the Blog pages show at most setting in Administration > Settings > Reading.

Don’t be confused by what an archive is–it is just a generated display of your posts at that moment. You don’t do anything to create the archive, that’s an automatic thing WordPress does for you. Usually, archives are date, category, tag, or author, based.

Access to archives is typically presented via links in a sidebar under an Archive (date based), Category, or Tag Cloud, heading. Widgets, or Template Tags, such as wp_get_archives(), wp_list_categories(), wp_tag_cloud(), and wp_list_authors(), are the constructs used to present links to users to visit your various archives. The process of placing code in your Theme’s Templates is explained in Stepping Into Templates and Stepping Into Template Tags.

Once a user clicks on a Category link in the sidebar, the display of those posts can be controlled by a Category Template. Other Templates, such as Author Templates, and Tag Templates, are available if you set them up. These Templates can be coded via Template Tags such as the_title(), the_content(), or the_excerpt(), to display just a post title, the full content of the post, or just an excerpt of the post.

Also, it is important to understand the Template Hierarchy, as that is how WordPress determines what Template to use to render the posts for reading by your readers.

If a user visits a Category archive, then clicks on a given post title in that Category archive, the display of that single post is again presented by another Template, and again, the Template Hierarchy determines what Template displays that single post. Finally, that single post Template can be coded to display just the title, the full post content, or an excerpt.

See:
WordPress Semantics

There’s no built in way to do this.

Conceptually – what you are saying is you only want certain posts on your main page. Thus the main page is not to be a full posts page. A way to accomplish this is create a category “Main Page”, and only show on the main page posts that are in that category. When you no longer want the post on the main page, take it out of the Main Page category.

If this approach sounds workable and you’d like to see some code that allows you to do this, post back.

I am having a similar problem. If you are still willing to share some code I would appreciate it.

Thanks