How do I know how much carbs, fat and protein I should be eating?

The MFP default goals are not terrible for most people, assuming they don't set a weight loss rate that's over-fast for the total amount they have available to lose. Why not set up your MFP profile, log your food, and see how close you come to the default goals?

Some of the "right" goal is personal, since satiation is individual, and there can be variation in nutritional needs to feel best. That part's a personal experiment, not something others can specify for you exactly.

In any case, you don't need to hit macronutrient goals exactly every single day. Pretty close, on average, is fine for nutrition and health.

If your goal is weight loss, nutrition isn't the directly vital thing, calorie level is. Sure, nutrition can have an indirect effect: If our nutrition is sub-par, our energy can drop, so we move less/rest more and burn fewer calories than expected; or under-nutrition can make our appetite/cravings spike, making it tough to stick to a sensible calorie goal. But the direct effect on weight is still via calories.

Don’t use percentages when trying to figure macros. You want to use for as a base, .7 g of protein to 1 g of protein per pound of lean body weight and .3g to .5 g of good fats per pound of lean body weight. You can fill the rest of your calories in with whatever you want as long as you hit those two targets.

Yeah, just start with the myfitnesspal defaults. It's 50C 30F 20P. Perfectly good place to start. It's a reasonable split, and you don't have to get it exact. I try to hit my protein and fat. Carbs can fall where they will. You'll find out your eating preferences with tracking and review.

You tell us nothing about you, so I'll say, start at, "Lose 1 pound per week," like the site suggests.

Set your "Activity Level" realistically. Anyone with any kind of job or who attends classes and/or lives a normal life including a commute and a home to clean is NOT sedentary, regardless of you sitting for part of the day. Don't choose "sedentary" unless you're homebound.

Then when you do any kind of purposeful exercise, enter it into the "Exercise" section and eat a little more to fuel that - like 200-400 calories more per hour of moderate exercise.

Here's the official explanation: https://support.myfitnesspal.com/hc/en-us/articles/360032625391-How-does-MyFitnessPal-calculate-my-initial-goals-

Best advice I was given was “just concentrate on your calories”

Because…
Say for example 2 bacon medallions are
67 calories…guaranteed it’s low fat,low carb, high protein (well sort of)

A bag of malteasers will probably be say 260 calories for 100g which will have lots of carbs and fat…and won’t fill you up for very long

You will get the hang of it you can look under nutrition how many carbs/fats/protein you are having

But just calorie count…

You can lose weight just concentrating on not exceeding your calorie goal. I did that quite successfully. You need to pay attention on days where you are feeling hungry all the time, and take a look at your macros for that day and compare to the days you are not hungry. That will give you more insights into what sort of macro breakdown works best for you. For me protein fills me up quickly, and fat keeps me full longer. Carb heavy foods, even ones with lots of fiber, fill me up, but I am hungry again in an hour or two where a meal with a good amount of protein and fat will fill me up just as fast and leave me feeling full for many hours sometimes to the point of forgetting I should probably eat. That is not the case for everyone, so do some personal experimenting all while keeping within your calorie goal and see what works for you. Note, for me the least satisfying and shortest lasting things are foods that are high in carbs (usually simple carbs like the malteaser example above) and fat. They might give a quick hit of satisfaction, but it fades almost immediately. Potato chips are another example of that for me.

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