Log into your WordPress dashboard and in the dashboard menu under “Posts” select “Categories.” Add a new category such as “Press Releases” and enter “press-releases” as the slug. Click the “Save Menu” button. Repeat this procedure if you need to add more new categories.
Make sure that you have already setup a website navigation menu for the front-end of your website.
On the dashboard menu under “Appearance” select “Menus.” Under “Categories,” select to “View All” of the available categories which you have added. Click the check box next to the particular category title that you want to add as a menu topic to your navigation menu, and then click the button that says “Add to Menu.” Drag the menu topics into your desired order within the Menu. Save.
Whenever you create a blog post, select the category or categories where you would like to see your particular post grouped. Then, publish or update your post.
On the front end of your WordPress website, you should be able to select the menu-category and all of your posts that you assigned to that particular category will appear on the same page, usually in the order of the most recent posts first near the top. In other words, each category is like an archive of all the posts to which the particular category has been assigned.
When you customize your site for where blog entries and articles are posted, you can setup a static front-page and select a different web page on your site (or possibly no page at all) where all your posts will appear regardless of category assigned. I will need to test the “no page selected for blog posts” scenario.
Here is a much more detailed article on the topic, including organizing into sub-categories.