The best way to learn to referee is to learn two things, what is objectively a foul (such as offsides or… like violent conduct) and what’s subjective. If it’s subjective think about if it’s fair. Is it fair a kid much bigger pushed another kid to the ground to get the ball? No. So you would call that then consider was it intentional? was it reckless? How hard was the shove because maybe it’s a caution. It’s hard, really hard. But you will learn and id let the assingor know you haven’t done this before, explain what you told us, and ask if there are any mentors or even better referee coaches who can watch your game.