Include only one category in category link menu

Hi,
I am making a portfolio site that each portfolio is a category and each project is a post, for example:

Construction category has projects: interior, exterior
Painting category has projects: acrylic, oil
Remodeling category had projects: bathroom, kitchen, basement
and the list goes on and on.

The reason I don’t make these as pages is that I want to use the next and previous functionality for projects, so once you are on Interior post you can use arrow to next post which is Exterior .

I also have a page called News and this is also a category and of course has posts in it that are time-based.

Now, I want News category uses all the functionality of Category and Archive link sidebar menu and shows only news posts and not my portfolio projects posts.

Now, the question is how to exclude all my project categories and posts from this sidebar.(in another words include only news posts)

If you are suggesting some pieces of code to modify or add, please please tell me what file it is in and explain it well as I am not php savvy very much.

Thanks for your unconditional help and advice ??