Masonry Layout

I’m completely new to php and am having trouble. I’m trying to create a magazine layout that consists of a featured post slider and posts that are in 3 columns and are layed out with set widths.

Basically heres what I want the posts layout to look like:
https://www.nylon.com/

I have no clue how to get started. I created a seperate php page for the posts that I call into the homepage via:
<?php get_template_part(); ?>

I basically need to know how to call my posts by categories and lay them out like the link above.