How to fetch later posts in a different format

Hello there,

I am currently working on an adaptation of a free wordpress theme. My intent was to modify it enough to have a bespoke website for my personal needs. I am having great success, despite me being new to php code and generally wordpress.

My plan is, which is half implemented, is to have posts in a featured banner running along the top of my website before the navigation. There will be a minimum of 8 of this type and they will only be showing images which you can click to access the post page and read the article. Beyond this, I wanted to show a remaining 4 posts from the archive in a different format.. preferable a title, image and text below.

This is all on the index page at the minute.
I need help implementing this.. as I cant figure out how to fetch posts past number 8. My loops keeps showing the latest ones.
Any help would be great thanks