Home showing only posts from one category or tag

Hi.
I’m using the Imbalance 2 theme from wpshower and I’m trying to change the homepage to display only the latest posts from a specific category. It would also work to have it show posts with a specific tag. I’ve searched the forums for answers and found a few topics about this issue, but most were outdated and the rest wouldn’t work, or at least I couldn’t get them to work.
Can anyone give me a hint about this?
Thank you very much.