Posting to specific pages

Hi
I am struggling to connect my posts to appear on a certain page. they just appear on a random page on the website. How can I link a certain category posts to a certain page?
Is there a widget or plugin that can make this easier?

I have a page navigator and would like each category to appear in a certain drop down area.

The reason why I am asking is if I can do this I can update my website via the worpress app on my phone by just posting photos under a certain category and it appears under the right page.

Can you please assist?