Posting on both my homepage and on my page/menu's

Hi,
I have just created all of my menus (and sub menus) which appear in a banner at the top of my site. However when I now go to write a new post, it doesn’t give me the option of what page I want to put it under, so it only appears on the homepage (whereas I want it to appear on both the homepage and on the specific page category.
Thank you!