From calories to grams
A macro split is just a way of dividing your daily calories. Once you pick percentages for carbs, protein and fat, the math is simple: calories times the percentage gives calories per macro, then dividing by 4 (protein and carbs) or 9 (fat) converts to grams. Because fat is more calorie-dense, a small change in fat percentage moves more calories than the same change in carbs.
Making macros work day to day
Hitting your protein target matters most, since it supports muscle and keeps you full; carbs and fat can flex around training and preference. Use a food app to learn the macros of meals you eat often, aim to land close rather than perfect, and revisit your calorie target every few weeks as your weight changes.